Magnetoplasmadynamic processor, applications thereof and methods

ABSTRACT

Embodiments of magnetoplasmadynamic processors are disclosed which utilize specially designed cathode-buffer, anodeionizer and vacuum-insulator/isolator structures to transform a working fluid into a beam of fully ionized plasma. The beam is controlled both in its size and direction by a series of magnets which are mounted in surrounding relation to the cathode, anode, vacuum insulator/isolators and plasma beam path. As disclosed, the processor may be utilized in many diverse applications including the separation of ions of differing weights and/or ionization potentials and the deposition of any ionizable pure material. Several other applications of the processor are disclosed.

BACKGROUND OF THE INVENTION

.[.This application.]. .Iadd.This is a continuation of copendingapplication Ser. No. 07/387,977 filed on Jul. 28, 1989, now abandoned,which is a reissue of Ser. No. 06/512,728, filed on Jul. 11, 1983, nowU.S. Pat. No. 4,682,564, which .Iaddend.is a C-I-P of application SER.No. 210,241 filed Nov. 25, 1980, now abandoned.

FIELD OF THE INVENTION

The magnetoplasmadynamic phenomena was first discovered in 1961 byapplicant and described in U.S. Pat. No. 3,243,954. A device that wasdesigned and tested was intended for space propulsion applications andis commonly known as a plasma propulsion system. The principal designand performance requirements were to fully ionize a single species vaporand accelerate all the ions to a preferred high velocity into space. Thedevice was to have high thrust efficiency, where thruster efficiency wasdefined as

    Thrust efficiency=ηmassηexhaustηpower

where ##EQU1## and .sup.η exhaust=exhaust efficiency=v/v_(max) and##EQU2## where

    m.sub.ions =mass flow of ions

    v=average velocity of ions

See Table (5) for typical values

No attempt was made to separate materials in this process as theintended application did not direct the development to that end.

Subsequent to the issuance of the above discussed patent, applicantreceived, as sole patentee or co-patentee 7 U.S. patents which arebelieved to be only very generally related to the subject matter of theinstant patent application. U.S. Pat. No. 3,309,873 was a CIP of U.S.Pat. No. 3,243,954 and disclosed a fourth embodiment of accelerator overand above the three embodiments of accelerator disclosed in U.S. Pat.No. 3,243,954. This fourth embodiment discloses a plasma accelerator foruse at channel pressures of about 1-10 mm. HG.

Subsequently U.S. Pat. No. 3,388,291 was issued and constituted afurther refinement on the above discussed two patents. This patentbroadly introduced the concepts of (1) the anode sheath, (2) the cathodejet, and (3) the electric ram jet but as pertains to the instantinvention lacks the refinement and detail as well as the bufferstructure, isolator structures, multiple magnet structure and gasinjection details of the instant invention.

Subsequently, U.S. Pat. No. 3,413,509 was issued and this patentgenerally disclosed the concepts of (1) the cathode buffer, (2)injection of feed gas near the anode, and (3) opposed electrodeconfinement, none of which were disclosed with the specificity disclosedherein. As pertains to the instant disclosure, that patent lacks thephysical structure of the present processor and as such has mechanicalconfinement limitations. Further, there is no disclosure therein of thedecisive and critical implications of the minimum voltage hypothesis.

Subsequently, U.S. Pat. No. 3,453,469 was issued which is related toabove discussed U.S. Pat. No. 3,413,509 as both patents matured fromapplications which were C.I.P.'s of prior application Ser. No. 458,837filed May 20, 1965. This patent disclosed the concepts of (1) plasmacontainment with opposed electrodes, and (2) mechanical pumping out ofthe apparatus chamber from a plurality of locations, each of which lacksa sophistication of the present invention. Application Ser. No. 458,837matured into U.S. Pat. No. 3,453,488 and further U.S. Pat. No. 3,453,474was also a C.I.P. of Ser. No. 458,837.

Finally, U.S. Pat. No. 3,467,885 was issued and disclosed the conceptsof (1) open ended plasma confinement, (2) the equation for the length ofthe cathode jet and (3) sonic jet details.

Regarding the above discussed patents, it is noted that they teach someof the basic concepts disclosed herein and the instant inventionprovides the sophistication to enable the practice of the hereindisclosed applications. Again, while the above discussed patents arebelieved generally related to the instant invention, their pertinence tothe instant invention may be best characterized by the degree ofsophistication of the concepts taught herein as opposed to therein. Forexample, prior U.S. Pat. No. 3,453,469 discloses a plurality of pumpsfor evacuating the chamber, each mechanical in nature whereas, herein,mechanical, sorption, condensation and ion pumps are disclosed. Manyother such examples will become self-evident through comparison of thisapplication with the subject matter disclosed in the prior patents. Noneof prior patents disclose for example the vacuum insulator/isolatorconcepts taught herein.

The magnetoplasmadynamic phenomena herein described is simply thecontrolled interaction of a high current electrical discharge and anapplied solenoidal magnetic field through the induced current andmagnetic field resulting when the plasma is produced, confined andaccelerated by the applied electric and magnetic fields. This type ofinteraction phenomena is referred to as the Hall Current effect. Thesignificance of the work of Cann and others lies in:

(a) the development and appreciation of the mechanisms ofelectromagnetic acceleration and confinement;

(b) the development of a global understanding of the thermodynamicsresponsible for minimizing the system free energy and expressing theserelations in terms of a minimum voltage hypothesis;

(c) correlating experimental data in terms of the above; and

(d) the development of design concepts using the above items to optimizeperformance of a space plasma propulsion engine.

The proper voltage selection and propellant injection rate resulted inionization and acceleration of the charged particles (ions andelectrons) in the direction parallel to the applied magnetic field. Tileresulting plasma was accelerated to the desired exhaust velocity. Otherprior art is also known to applicant. For example, Janowiecki, et al.,U.S. Pat. No. 4,003,770 (also United States Patent Office VoluntaryProtest Program Document No. B 65105) discloses a process for preparingsolar cells in which p- or n-doped silicon particles are injected into aplasma stream where the particles are vaporized. The heated particlesare then discharged from the plasma stream onto a substrate to provide apolycrystalline silicon film. During the heating and transport, asuitable atmosphere is provided so that the particles are surrounded toinhibit oxidation. However, Janowiecki, et al. do not suggest the use ofhis techniques for refining the silicon. Walter H. Brattain in U.S. Pat.No. 2,537,255, discloses the deposition of silicon for silicon photo-emfcells, using a mixture of hydrogen and silicon tetrachloride. However,this early technique does not disclose the use of a magnetoplasmadynamiceffect for either production of these solar cells, nor the refining ofmetallurgical grade silicon into semiconductor grade silicon.

Tsuchimoto in U.S. Pat. No. 3,916,034 discloses a method fortransporting semiconductors in a plasma stream onto a substrate. Theplasma is directed by magnetic fields onto thin film substrates.Tsuchimoto is typical of prior ionization chambers for use with amagnetogasdynamic process. In that magnetogasdynamic process, massutilization efficiency is low, making the method ineffective forrefining mass quantities of silicon. All species are not normallyionized because no preferential ionization can be accomplished with thisinvention. That is because the dopants are mixed externally from theionization chamber by switching the magnetic fields. Tsuchimotodiscloses a device having severe limitations as compared to the instantinvention. He discloses the surface area of deposition as on the orderof 1 cm², the discharge current as 1-3 amps, the pressure in the plasmasource chamber as 10⁻² Torr and the tolerance of the cathode to thepresence of oxidizing material is quite low. As Will be seenhereinafter, each of these disclosed aspects of the Tsuchimoto deviceare vastly different from the teachings of the present invention.Further, Tsiichimoto is believed non-pertinent because:

(1) be requires a separate cathode filament heater in order to sustaindischarge;

(2) his plasma is not uniformly electromagnetically accelerated to acontrollable energy; in his discussion the prior art, he implieselectrostatic acceleration;

(3) his discharge voltage of 200-300 volts differs from that of thepresent invention;

(4) his typical power levels of 300-900 watts differ;

(5) col. 7, lines 26-48 indicate a lack of purification of the ion beam.

Other distinctions are also present which are believed relevant but forreasons of brevity are not pointed out herein.

Further, applicant is aware of IBM disclosure Vol. 19 No. 5 (1976) to P.C. Karr. This disclosure gives few if any specifics on operatingparameters and is distinct from the instant invention in at least thefollowing particulars:

(1) No specifics of the control of coils 11, 12, 13 are given), onlygeneral statements as to their purpose. Herein, the description of theelectromagnets is given both theoretically and in exemplary form;

(2) The plasma is transported through a "rippling" technique whereas,herein, electro-magnetic axisymmetric acceleration is used;

(3) There is no disclosure of the separation of impurities or unwantedions simultaneously with deposition. Herein, this is accomplished.

Again, for brevity, other distinctions are not pointed out herein.

Several references disclose glow discharge techniques used in depositionprocesses, For example, Cohen-Solal, et al. U.S. Pat. No. 4,013,533 isdirected to a glow discharge sputtering process. Aisenberg, U.S. Pat.No. 3,961,103 is directed to a glow discharge system and subsequent ionbeam deposition.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a plasmaprocessor in which a working fluid is transformed into a neutral beam offully ionized plasma with the ion flux rate thereof being higher than 50amperes equivalent.

It is a further object of the present invention to provide a plasmaprocessor in which the plasma formed therein may be controlled both asto size and direction thru the combined use of electric and magneticfields.

It is a still further object of the present invention to provide aplasma processor which is designed to remain electromagnetically as wellas plasma dynamically stable over a wide range of controllablevariables.

It is a yet further object of the present invention to provide a plasmaprocessor wherein the plasma ions formed thereby are monoenergetic andthe energy level can be controlled within defined limits.

It is a yet further object of the present invention to provide a plasmaprocessor which is operable in steady-state fashion for hundreds ofhours or more.

It is a yet further object of the present invention to provide a plasmaprocessor with high mass utilization, power efficiency and processingrate.

It is a still further object to provide a plasma processor which may beadapted to perform ill the following applications:

(a) processing of an inert gas for annealing surfaces, film and layeredstructure;

(b) processing of a chemically active gas to perform etching operationsor otherwise react with a deposition surface;

(c) processing and deposition of any pure material which may be ionized;

(d) processing and deposition of a material which will form a compoundor mixture or act as a dopant to the substrate material;

(e) simultaneous deposition of two or more substances of comparableionization potential;

(f) simultaneous deposition and annealing;

(g) deposition of conductors on semiconductor wafers or films;

(h) separation and purification of a component of a compound that has alower ionization potential than another component thereof;

(i) collection and deposition of the separated and purified component;(j) utilization of axisymmetric mass spectrograph feature of processorto separate materials of different mass and comparable ionizationpotential;

(k) collection and deposition of the so separated materials;

(l) space propulsion;

(m) function as a component of a linear magnetic mirror fusion machine;

(n) convert thermal or kinetic energy of plasma into electrical energy,when operated as an MPD generator using a fully ionized plasma as theenergy source.

Further objects of the present invention include the following:

It is an object of this invention to make thin doped semiconductorcrystals rapidly and cheaply.

It is a further object to make various semiconductor transistor, diodes,resistors and capacitors rapidly and inexpensively. It is a particularobject to make these various semiconductor and thin film devices in sucha way that large areas of the semiconductors may be inexpensivelyproduced.

It is, accordingly, an object to provide a method and apparatus forrefining silicon, and particularly for refining matallurgical gradesilicon into a purer form of silicon to produce semiconductor gradesilicon.

It is a further object to produce semiconductor grade material in thinFilms having large areas, thereby providing an inexpensive base productfor making silicon photovoltaic solarcells.

It is a further object of this invention to provide a method of refiningmaterials such as silicon in layers using magnetoplasmadynamictechniques.

Accordingly, it is a further object of the present invention to providea new and improved method and apparatus for the separation of materialswhich does not depend upon conventional chemical reduction processes,conventional catalytic processes, vapor transport processes, laserbeating, differential ionization, electron beam beating or a meltedcrystal pull process to obtain separation of species. However, a furtherobject of the invention is to provide a new and improved means ofelectromagnetic separation by selective ionization and acceleration in amagnetic field as well as by utilizing the axisymmetric massspectrograph separation techniques unique to this device. Particularlyit is an object to provide a method and apparatus which has a low costrelative to present separators and which requires less power to operate.

It is a further object of the present invention to provide a means toform large area silicon films used for solar cells, and particularlylarge area silicon solar cells in a process which is economical tooperate and which has a low power consumption.

It is still a further object to refine silicon for solar cells to beused in terrestrial applications in which the cost of production of thesolar cells, and particularly the power consumption costs of production,are significantly less than the value of the power expected to beproduced by the solar cells during the lifetime of the solar cells.

Accordingly, the invention, in one aspect thereof, is directed to anapparatus for depositing materials in layers to form wafers and/or filmsof material by means of magnetoplasmadynamic deposition. A plasma beamis electro-magnetically accelerated in a vacuum chamber by means of amagnetoplasmadynamic generator comprising a cathode, an anode, anaccelerating magnet adjacent to the cathode, a trimmer magnet adjacentto the anode, and a focusing magnet. The focusing magnet has a magneticflux pattern which can be rotated so as to direct the plasma beam indifferent directions as the plasma is ejected from the plasma generator.In one aspect of the invention, a means is provided for injectingmaterials into the plasma in order to create a modified plasma stream.These injected materials may comprise a carrier gas for the desiredionizable materials. The injected materials may also comprise dopantsused for depositing a doped layer of the material. The doped layer canbe of any desired thickness.

In another aspect, the focusing magnet may be placed on a gimbal so asto allow the magnetic flux field of the focusing magnet to be rotated,thereby permitting deposition of materials evenly on various portions ofthe target area.

In yet a further aspect of the invention, the apparatus is used todeposit a substrate before the semiconductor material is deposited.

In yet a further aspect of the invention, the material to be depositedis provided in the form of a hollow cathode. The dopant and carrier maythen be injected so as to pass through the hollow cathode as the dopantand carrier enter the plasma stream.

In yet a further aspect of the invention, the apparatus is used todeposit a substrate before the semiconductor material is deposited.While the semiconductor material is deposited, doped layers of thesemiconductor material are applied by the magnetoplasmadynamicgenerator. A top terminal may then be electro-deposited by the plasmagenerator onto the semiconductor material. This top terminal may beformed by mechanically placing a metal strip or grid on top thesemiconductor and bonding the metal with a material which is applied byelectrodeposition using the plasma generator.

In still another aspect, this invention is directed to a method forproducing semiconductor materials such as semiconductor grade silicon ina vacuum environment.

A plasma is established between a cathode and an anode. The plasma isaccelerated with an accelerating magnet and focused onto a depositionarea located on a target area with a focusing magnet. The semiconductormaterial, such as silicon, is placed in the plasma, thereby forming theplasma stream.

The deposition area may be moved along the target area by changing theflux orientation of the focusing magnet.

In yet another aspect, the completed semiconductors or semiconductorfilms may be removed from the target area by a robot means so thatsubsequent semiconductors or semiconductor films may be formed withoutthe requirement that the vacuum chamber be pumped down each time a newsemiconductor film or unit is to be formed.

In yet a further aspect of this invention, metal terminals such asaluminum terminals may be formed on semiconductors bymagnetoplasmadynamic-deposition techniques.

Other aspects of the invention such as, for example, details of thetrimmer magnets and vacuum insulator/isolator structure will bedescribed in great detail hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a schematic representation of the relationship between acathode, anode, electromagnet and anode sheath.

FIG. 1b shows a "wire model" of the representation of FIG. 1a forinduced field analysis.

FIG. 2 shows a graph of computed Hall wire currents and thrusts.

FIG. 3 shows the performance characteristics of the magnetoplasmadynamicsource when SiCl₄ is the silicon source material.

FIG. 4 shows the performance characteristics of the magnetoplasmadynamicsource when SiH₄ is the silicon source material.

FIG. 5 shows the performance characteristics of the magnetoplasmadynamicsource when the silicon source material is silicon per se.

FIG. 6 shows a graph of voltage versus time for dual mode operation.

FIG. 7a shows a graph of mass flow rate versus time for singly ionizedLithium;

FIG. 7b shows a graph of mass flow rate versus time for doubly ionizedLithium;

FIG. 8 shows a schematic representation of a first embodiment ofmagnetoplasmadynamic device according to the invention.

FIG. 9 shows a schematic representation of the arc-forming section ofthe embodiment of FIG. 6.

FIG. 10 shows a block diagram representing a process of formingsemiconductor films in accordance with the invention.

FIG. 11 shows a side schematic representation of a further embodiment ofmagnetoplasmadynamic processor;

FIG. 12 shows a cross sectional view thru the line 12--12 of FIG. 13

FIG. 13 shows a cross section through the anodeionizer.

FIG. 14 shows a schematic view of the magnetic flux lines generated bypassing current through the coil as indicated.

FIG. 15 shows a schematic view of plasmadynamic forces on the plasma.

FIG. 16 shows a schematic representation of electric current paths.

FIGS. 17-19 show schematic representations of the flow paths for atoms,electrons and ions with FIG. 19 being a cross sectional view along theline 19--19 of FIG. 18.

FIG. 20 shows a graph of species concentration ratios for decomposingSiCl₄.

FIG. 21 shows an embodiment of processor particularly adapted to processsilane feedstock, and shown with deposition target.

FIG. 22 shows a device similar to that shown in FIG. 21, shown withstructure designed to separate ions of differing molecular weights.

FIG. 23 shows a cross-sectional view of the processor of FIG. 22,showing how the differing ion trajectories enable separation to occur.

FIG. 24 shows a graph of deposit thickness versus radial position for acollector of approximately one square meter in area mounted downstreamof the processor.

FIGS. 25 and 26 show end and side views respectively of a Gaume typesolenoid electromagnet.

FIG. 27 shows a graph of magnetic field strength versus distance fromsubstrate to cathode-buffer for the present invention.

FIG. 28 shows a detailed view in cross-section of the cathode-buffer.

FIG. 29 shows a schematic view of the gas supply systems for thecathode-buffer and anode ionizer.

THEORETICAL BASIS FOR INVENTIVE CONCEPTS TAUGHT HEREIN ION PRODUCTION

The momentum conservation equations indicate that some torque and forcereaction must occur on the processor during operation thereof. For thisto happen, ions must be produced in and expelled from the device withboth axial and angular velocity. The lower the ion flux rate, the higherthe resultant velocities must be and, consequently, the beam power mustbe higher. On the other hand, as the ion production and expulsion rateincreases, the power in ion production becomes very high; hence some ionflow rate must exist at which the electrical power into the discharge isa minimum. If the arc current is held fixed, this implies that thedischarge seeks a minimum voltage Anode in which to operate. The aboveargument then indicates that the arc accomplishes this end by ionizingthe optimum amount of material thru-put to expel in the exhaust beam.The key, then, to explaining the operating characteristics of the devicelies in determining the optimum ion exhaust rate and in understandingthe production process for these ions throughout the volume of thedischarge.

Atoms are not confined to any great extent by the electric dischargeand/or applied magnetic field. Hence the flow field of the gas will besubstantially the same as one would find for the gas issuing from theorifice with no discharge present. The discharge must now encompass thisgas and adjust the electron temperature and density throughout itsvolume so as to ionize the optimum amount of material. Clearly, to getgood material utilization, the injected flow rate should be close to theion flow rate in the beam. However, in the interest of obtaining bestoverall efficiency, it may be necessary to inject slightly more materialthan is used by the beam. This would help to restrict the volume of thedischarge and perhaps keep the electron temperature to lower values,thus reducing power loss by electron energy convection to the anode.

Since a significant number of atom-electron collisions are elastic(non-ionizing) collisions, the energy used to ionize one atom must beconsiderably greater than the ionization potential of the atom. Theenergy difference is transferred into the internal energy of the atomsand ions. If most of the injected mass is eventually ionized, thisenergy is not lost, but is available to be transferred into beam kineticenergy by eventual expansion through a magnetic nozzle to be describedhereinafter. It is obvious, of course, that this internal energy of theheavy particles can never be higher than that of the electrons. Thisargument indicates that the ionization process need not be efficient.However, the number of inelastic collisions that excite the electrons tostates that can radiate should be minimized. This is basically a problemof working fluid selection.

The electron internal energy results from the electron current passingthrough the potential drop and being randomized by collisions with heavyparticles. For this reason it would be expected that the highestelectron energy would be found ill the anode sheath, after the electronshave fallen through most of the potential drop. This is fortuitous,since it is precisely in this region that the highest ion productionrate is wanted, to let the ions gain a maximum of kinetic energy byfalling through the potential back toward the cathode jet. However, someions must be produced near the cathode attachment area. These ions mustbe accelerated downstream in the cathode jet against the axial electricfield. This is accomplished by collisional transfer of momentum from theelectrons which have obtained the momentum from j×B forces.

ION ACCELERATION

In the discussion to follow, the following definitions are applicable:

|e|=charge on the electron

E_(r) =radial electric field

E_(z) =axial electric field

u_(I) =radial ion velocity

v_(I) =azimuthal ion velocity

w_(I) =axial ion velocity

B_(r) =radial magnetic field strength

B.sub.θ =azimuthal magnetic field strength

J_(r) =radial current density

J.sub.θ =azimuthal current density (Hall Current density)

J_(z) =axial current density

σ=electrical conductivity

P_(o) =ambient pressure at outer edge of anode sheath

P_(i) =ambient pressure at inner edge of anode sheath

μ_(o) =permeability of vacuum

I=total electric current in the electric discharge (arc current)

R_(as) =average radius of annular anode sheath

n_(I) =number density of ions

u=radial velocity of plasma

u_(e) =radial velocity of electrons

w_(e) =axial velocity of electrons

Momentum can be transferred to the ions from electric fields or fromcollisions with other particles. For convenience, the momentum exchangeprocesses in a fully-ionized gas through which an electric discharge ispassing shall be discussed.

Locally, the force on each ion is given by the following expressions:

    Axial: F.sub.z =|e|{E.sub.z +μ.sub.I B.sub.θ-v.sub.I B.sub.r -J.sub.z /σ}          1

    Radial: F.sub.r =|e|{E.sub.r +v.sub.I B.sub.z -w.sub.I B.sub.θ -J.sub.r /σ}                          2

    Azimuthal: F.sub.θ =|e|{w.sub.I B.sub.r -u.sub.I B.sub.z -J.sub.θ /σ}                          3

If an electric discharge is established in a uniform axial magneticfield we shall call the region where the current flows downstream the"anode sheath" and the region where it flows upstream the "cathode Jet."If a cathode of maximum diameter R_(c) is surrounded by an anode ring ofdiameter R_(A) (R_(A) >R_(c)) we ask the questions:

1. Does the cathode jet expand out to meet the anode sheath?

2. Does the anode sheath contract in diameter to meet the cathode jet?

3, Do both (1) and (2) occur simultaneously?

Consider First the cathode jet. If the cathode jet is to expandoutwardly, conservation of momentum states that the axial momentum ofthe jet must increase and the rotational momentum of the jet mustincrease. However, the local (E+v×B) axial and tangential electricfields are both in the wrong direction to accelerate the ions and themomentum must hence be transferred to them by electron collisions. Thisis a highly dissipative process, resulting in strong heating of theelectrons. This increases the rates of entropy production over thatcaused by ion-electron drag in a purely dissipative plasma (no bodyforce).

In the anode jet the situation is quite different. Both E_(z) and u_(I)B.sub.θ are in the positive z coordinate direction, thus helping toaccelerate the ions axially. The only dissipative or entropy productingprocess is that associated with the electron-ion drag. Similarly, in theazimuthal direction the local electric field u_(I) B_(z) aids the Hallcurrents in spinning up the ions. This allows the Hall currents to besmaller and thus dissipate less energy in spinning up the gas to therequired velocity. These rather crude arguments indicate that if thedischarge tends to operate at a minimum potential, then the current inthe anode sheath would tend to move inward to meet the cathode jet,rather than vice versa.

Further strength is lent to this argument when the radial force balanceon the anode sheath is investigated. Assuming that no radial force canexist on the anode sheath as a whole, an integral of the radial momentumequation gives the following relation: ##EQU3## where P_(o) -P_(i) =thepressure difference across the sheath.

R_(AS) =average radius of the anode sheath. This equation indicates thatHall currents must exist in the anode sheath for it to maintain itsradial equilibrium. The Hall currents can be induced, however, only ifthe anode sheath moves radially inwardly across the magnetic fieldlines, i.e., ##EQU4##

In the more general case where the solenoidal magnetic field diverges,rather than being uniform

    -J.sub.θ =σ(u.sub.e B.sub.z -w.sub.e B.sub.r)

From the above discussions we postulate a model for the device asfollows when it is operating in a magnetic field that is initiallypurely axial and then, at some distance (z>L) downstream, is made todiverge.

1. A uniform diameter cathode jet is established which carries only asmall fraction of the injected mass flow rate.

2. An annulus of plasma is established off of the anode face. Theinjected mass is accumulated within this annulus. All of the dischargecurrent initially passes through the annulus, either distributed fairlyuniformly azimuthally or as a concentrated spoke, spinning aximuthallyat a high velocity.

3. The average radius of this anode sheath decreases downstream. Thiscauses the ions in the sheath to be accelerated slightly in the axialdirection and to be spun up to high azimuthal velocities. The electronsare simultaneously heated, mainly by the ion-electron drag in theazimuthal direction, where the azimuthal electron motion is helping tospin up the ions.

4. At axial positions near the electrodes, and even some considerabledistance downstream, a significant potential drop exists and must besupported between the cathode jet and anode sheath (can be over 50% ofthe potential difference across the electrodes).

5. The anode sheath eventually meets the cathode jet at z=L and thecurrent path is completed. No discharge current flows at axial positionsbeyond this point, at which time the axial electric field in the cathodejet goes thru a zero.

6. At positions of z>L. the magnetic field acts like a magnetic nozzle.As the field diverges the ions are accelerated axially by two processes:

a. Conservation of angular momentum requires that as the jet radiusincreases, rotational ion energy must be transferred to axial and radialkinetic energy.

b. The high energy electrons tend to expand out of the nozzle ahead ofthe ions, thus setting up a positive axial electric field thataccelerates the ions. In this manner, all of the energy of the particlesin the beam can be converted into the kinetic energy of the ions.Obviously, some of this energy will reside in the radial and azimuthalvelocity of the ions; however, a high percentage of the plasma beammomentum will be converted into axial motion. The mathematical detailsof working out the implications and performance potential of a deviceworking with these postulated mechanisms is presented in the nextsection.

INTEGRALS OF THE MOMENTUM EQUATIONS

In the following discussion the following definitions are relevant:

P=plasma pressure

P_(oc) =pressure at outer edge of the cathode jet

R_(cj) =outer radius of cathode jet

J_(r) =radial current density

J_(z) =axial current density

B_(r) =radial magnetic field strength

B.sub.θ =azimuthal magnetic field strength

B_(z) =axial magnetic field strength

μ_(o) =permeability of vacuum

r=radial coordinate

z=axial coordinate

s=dummy variable

I=total discharge current

d(vol)=volume element

dS=surface clement

A.sub.θ =vector potential

Ψ=scalar potential

ω_(e) =σ|B|/|e|n_(I)

There are a few cases where the net electromagnetic force in anaxisymmetric body can be computed without detailed knowledge of thedistributions of current and magnetic field. In the general case, themomentum equations must be integrated simultaneously with continuity,energy, Ohm's laws, Maxwel's equations and the equations of state, Thecases chosen here are such that the integrand (force-per-unit volume)can be put into the form of a divergence, by using Maxwell's equationsand simplified momentum equations. These forces can be integrated interms of total current, radius, and applied magnetic field.

Pressure Due to J_(z) B.sub.θ Pinch

Here the average pressure on the cathode is computed in terms of thecurrent and radius of attachment.

The equations used are a momentum equation

    p/dr=-J.sub.z B.sub.θ. p(r=R)=P.sub.σ          6

an induction equation

    1/rd/dr(rB.sub.θ)=μ.sub.o J.sub.z. B.sub.θ (r=0)=0.sub.1 7

a total current integral ##EQU5## and a definition of average pressure##EQU6##

Combining the above reactions, it follows that independent of thedistribution of J_(z), the average cathode pressure is given by:##EQU7##

The pressure given by Eq. 10 will act on the cathode to give a thrust.This thrust force is given by μ_(o) I² /8π and is independent of thedistribution of the current density at the cathode, and of the size ofthe cathode attachment.

Thrust Due to J_(r) B.sub.θ Pumping

The amount of thrust in an axially symmetric volume due to radialcurrents and induced azimuthal magnetic field can be evaluated in termsof the magnetic field distribution at the boundaries. This, in turn,call be evaluated from the total currents. The following relations areused: ##EQU8## From Eq. 12 it follows that J_(r) B.sub.θ =-∂/∂z(B.sub.θ² /2μ_(o)) ##EQU9## B.sub.θ can be found by integrating Eq. 11:##EQU10##

Equation 13 shows that thrust can be evaluated in terms of magneticfield and Eq. 7 shows that magnetic field depends only upon axialcurrent. If:

(a) Current leaves cylindrical anode of radius R_(A)

(b) Current enters circular cathode of radius R_(c) with uniform currentdensity then ##EQU11##

Torque Due to (rJ_(z) B_(r) =rJ_(r) B_(z))

In an axially symmetric volume with radial and axial currents andmagnetic fields, there will be a torque which occurs when the currentcrosses the magnetic field. To evaluate this torque, introduce thevector potential A.sub.θ.

    B.sub.r =-(∂A.sub.θ /∂z)B.sub.z =(1/r)(∂/∂r)(rA.sub.θ)    16

The quantity (rA.sub.θ) is constant along a magnetic field line. Thetorque-per unit volume is given by: ##EQU12## where ∇.J=0 has been used.Upon integration over a volume R of surface S, outward normal n##EQU13## If rA.sub.θ is constant at anode and cathode ##EQU14## Finallyfor a point cathode, and an average axial field B_(z) through a circularanode of radius R_(A),

    Torque=1/2BIR.sub.A.sup.2                                  21

Max Thrust Due to J.sub.θB_(r)

In an axially symmetric volume where J.sub.θ is induced (by the Halleffect), the amount of axial force cannot be larger than for the case ofa completely diamagnetic plasma. In this limiting case, the J.sub.θ liescompletely in the surface of the volume, and no magnetic fields existinside the volume. The currents and magnetic field are computed asfollows: Let B-B₀ +B₁, where B₀ is the applied field due to externalmagnets and B₁ is the field due to induced currents within the volume.Outside of the plasma, ∇XB₁ is zero, hence B₁ =∇Ψ is a scalar field.Since ∇.B₁ =0, then

    ∇.sup.2 Ψ=0 (outside of plasma)               22

Since B.n=0 at the plasma surface

    ∂Ψ/∂n=-(B.sub.0).n(at plasma surface) 23

In solving the Laplace Eq. 22 with boundary condition of Eq. 23, theforce is given by

    Force=-∫∫(B.sub.0 +∇Ψ).sup.2 ndS    24

where n is an outward normal and S is the surface area of the plasma.

The same result can be obtained by the following method. Here we shallattempt to solve for the surface J.sub.θ distribution for a particularplasma configuration shown in FIG. 1a. We use a θ-Ohm's law (where Ψ_(e)is the Hall parameter for electrons). ##EQU15## and the inductionequations ##EQU16##

In Eq. 25 the coefficient Ψ_(e) /|B| does not depend upon magneticfield, since Ψ_(e) is proportional to |B|. We assume J_(z) and J_(r) areknown, based upon visual observations of the operation of theaccelerator. It appears that J_(r) =0, and J_(z) =total current dividedby cross sectional area of the anode jet (2πR_(a) δ). Thus Eq. 25becomes ##EQU17##

From Eq. 27 we see that B_(r) (and not B_(z)) is important forcalculating J.sub.θ. We can use the integral solution of Eq. 26 whichassumes no magnetic material is present: ##EQU18## When applying Eq. 28we use Eq. 27 for the value of J.sub.θ in the region of the anode jet,and the known J.sub.θ in the electromagnet. Thus, Eq. 27 becomes:##EQU19## Eq. 29 is an integral equation for the Hall current in theanode jet.

Exact solutions are not available for Eq. 29. An approximate solutionbas been obtained by lumping the distributed Hall currents J.sub.θ intoconcentrated currents. We will refer to this technique (FIG. 18) as the"wire model." The Hall currents are replaced approximately by hoopcurrents in a set of wires. The error of the lumping has been estimated,by changing the number of wires-per-unit length of the anode jet, andshown to be small.

The solution found was for infinite conductivity, or more precisely λ→∝where ##EQU20## This is the limit of a completely diamagnetic plasma.

To solve the wire model, the current density is concentrated into a setof wires (see FIG. 1B). Thus, the wire for the electromagnet coil bas acurrent I_(c), where I_(c) is equal to the number of turns times thecurrent in one conductor. The wires which carry the Hall currents in theanode jet carry a current of J.sub.θ, Hall.∇z.δ. The integral Eq. 29 isthus replaced by a set of simultaneous algebraic equations. In theinfinite λ case, which corresponds to infinite conductivity, B_(r) =0.Thus, (B_(r))_(j) =0, where j stands for one of the points shown in thewire model of FIG. 1B. ##EQU21##

Some solutions of Eq. 31 are shown in FIG. 2. The Kernel function LGdefined in Eq. 28 can be computed in terms of elliptic integrals.##EQU22## where E and K are elliptic integrals and K² =4rs/{(r+s)² +t²}. To simplify the computations, a function G_(planar) based upon a flatgeometry was used ##EQU23##

This is a good approximation to the Kernel function near the coil. Theelectromagnetic thrust can be computed either from the integral of theJ.sub.θ B_(r) forces in the jet or by the reaction on the coil.##EQU24##

For the example of FIGS. 1A and 1B, the integration was made over thecoil. The thrust is approximately 80 percent of the product of thecross-sectional area of the anode jet times the magnetic pressure whichwould exist along the centerline if there were no Hall currents. This isprobably an upper limit of the possible thrust.

When the induced magnetic field due to the Hall currents is smallcompared to the applied magnetic field, the axial force on the magnets(i.e. thrust) can be expressed approximately as:

    Axial thrust B.sub.A I(R.sub.A -R.sub.e.sup.1)             35

where

I=arc discharge current

B_(A) =magnetic field strength at the anode

R_(A) =radius of anode

R_(e) ¹ =effective radius of virtual cathode (less than R_(A))

This is a semi-empirical expression

Further Theory of Operation

When electrical discharges are operated with an axisymmetric electrodeconfiguration and solenoidal magnets, electromagnetic forces react onthe electrode system and magnet coil. This force is a maximum when thecentral electrode is the cathode. Since momentum must be conserved, anequal and opposite force must be transferred to some working fluid whichmay consist of:

(1) Material injected through the electrode system,

(2) Ambient material entrained into the discharge,

(3) Material eroded from insulators, and/or

(4) Material eroded from electrodes.

The electromagnetic force transferred to the gas call be expressed asfollows: ##EQU25## where I=current in the electric discharge.

B_(A) =average strength of an applied solenoidal magnetic field in theplane of the anode attachment region.

R_(A) =inner radius of the anode.

R_(C) =outer radius of the cathode.

R_(c) ¹ ="virtual" outer radius of the cathode-usually the radius of thecathode jet in the plane of the anode attachment zone.

μ_(o) =permeability of free space: 4π×10⁻⁷ (MKS).

This force is transmitted directly to the ions and electrons of theworking fluid that passes through the discharge. Collisions betweenatoms and electrons and/or atoms and ions may transfer some of thisforce to the neutral particles, especially at higher pressures. Power isconsumed by the discharge in order to accomplish this and an expressionfor the power consumed is shown below when only one species is presentin the working fluid: ##EQU26## where: P_(r) =Bremsstrahlung radiatedpower.

V=potential drop across the electrodes.

m=mass flow rate injected through arc chamber.

∇h_(g) =enthalpy increase of unionized gas.

e=charge on the electron.

V_(D) ¹ =fraction of dissociation energy/ion.

Σ_(i) V_(Ii) =ionization energy for atom ionized to the ith level.

m_(I) =mass of the ion.

V_(r) =voltage drop associated with line radiation in producing an ion.

P_(A) =power transferred to anode.

P_(k) =power transferred to cathode.

m₁ =mass flow rate of ions.

As mentioned in the previous section the power consumed is a strongfunction of the mass flow rate of ions and will go through a minimum asa function of the ion flux rate, m_(I), if ionization and accelerationare occurring in the same regions of space and accomplished with thesame electrical discharge. Let the ion flux rate at which this minimumoccurs be (m_(I))_(cr). Then, ##EQU27##

The basic mechanism by which the discharge achieves the desired ionproduction rate (m₁) is by volume ionization of atoms by electron impactchanged through adjustment of the electron temperature. When thedischarge is "starved" (insufficient flow rate of material with thelowest first ionization potential) the discharge usually increases involume, the voltage across the discharge increases, and the electrontemperature increases. If more than one species of atoms is present inthe material being fed through the anode, the higher electrontemperature may initiate first ionization of a second species. If onlyone species is present and it is not hydrogen, then the increasedelectron temperature may initiate second ionization of that material.Alternatively, the higher the electron temperature will increase theheat flux rate to the anode attachment spot. The heat flux rate may gohigh enough to cause evaporation of anode material. The discharge maythen ionize this material and inject it into the beam. A fourtheventuality may occur if the ambient pressure of some substance is highenough to ensure numerous electron atom collisions within the volumeencompassed by the discharge. The volume encompassed by the dischargemay increase by a large factor and the discharge may ionize the ambientmaterial and recirculate it in the tank. All of these modes of operationhave been observed in studies of space prpulsion engines.

The processor may be "starved" in a number of ways:

(i) The discharge current can be increased.

(ii) The strength of the applied magnetic field can be increased.

(iii) The mass flow rate of working fluid can be decreased. If any oneof these changes is effected while an engine is running in an unstarvedmode, the processor responds in a unique manner. To be specific, assumethat the processor is operating with lithium vapor as the working fluidand that the unstarved mode of operation is represented by an adequatesupply of litium singly ionized atoms. If the mass flow rate is reducedgradually, then the response of the processor is shown schematically inFIG. 6. Pulses of doubly ionized lithium ions are generated periodicallyaccompanied by a voltage pulse. The frequency of these pulses increasesas the mass flow rate is decreased until at some mass flow rate theprocessor ejects only double ionized lithium and the voltage remainsconstant at the upper level. When the processor is operating in thetransition regime the between these two levels, operation will be calleddual mode operation. (See FIGS. 6,7a,7b) The ions and neutral gasparticles can be coupled through collisions if the gas density is high.When the gas density is low they can be completely uncoupled, which weassume here. Hence:

    F=m.sub.I (v.sub.I)+(m-m.sub.1)(ν.sub.g)                39

Since

    m.sub.cr =m.sub.I =F.sub.EM /νcr and v.sub.g >>v.sub.I  40

We can identify

    ν.sub.I)=ν.sub.cr                                    41

The minimum voltage hypothesis thus leads to the following predictions:

(1) A minimum amount of mass flow rate m_(cr) must be available to thedischarge:

    (m.sub.I).sub.cr =F.sub.EM /ν.sub.cr                    42

(2) The exhaust velocity of the ions, v_(cr), will be uniform andconstant over wide ranges of operating conditions at: ##EQU28##

(3) The potential drop across the electrodes of the discharge will be:##EQU29##

Using some simplifying assumptions, these equations have been evaluatedfor a processor that singly ionizes silicon atoms. The results of thesecalculations are shown in FIGS. 3, 4 and 5 and associated data isdisplayed in respective tables 1, 2 and 3.

                  TABLE 1                                                         ______________________________________                                        Performance characteristics of the                                            Magnetoplasmadynamic source (see FIG. 3)                                      ______________________________________                                        Silicon Source Material = SiCl.sub.4                                          Anode radius (m) =        0.050                                               Cathode Radius (m) =      0.005                                               Substrate Radius (m) =    0.150                                               Anode Rad.-Virtual Cathode Rad. (m) =                                                                   0.020                                               Deposition Rate (micron/sec) =                                                                          3.000                                               At B = .25 Tesla:                                                             Approx. Substrate Temperature (°K.) =                                                            1569.190                                            Voltage =                 63.674                                              Current =                 820.870                                             Power (kw) =              52.268                                              Thermal Efficiency =      0.650                                               Power Loss to Cathode =   3.530                                               Power Loss to Anode =     6.299                                               Volume Power losses =     8.472                                               Mass Flow Rate (mgm sec), silicon =                                                                     491.973                                             Mass Flow rate (mgm/sec), Hydrogen =                                                                    0.000                                               Mass Flow Rate (mgm/sec), Chlorine =                                                                    2484.355                                            Power in Spin (kw) =      1.887                                               Power in Axial Velocity (kw) =                                                                          15.097                                              Power in Ionization Energy (kw) =                                                                       16.984                                              Pressure on Substrate (Torr) =                                                                          4.396                                               Minimum Arc Chamber Pressure (Torr) =                                                                   42.164                                              Maximum Arc Chamber Pressure =                                                                          111.224                                             Max. Silicon Partial Press. in Arc Chmbr. =                                                             22.245                                              ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Performance characteristics of the                                            Magnetoplasmadynamic Source (see FIG. 4)                                      ______________________________________                                        Silicon Source Material = SiH.sub.4                                           Anode radius (m) =        0.050                                               Cathode Radius (m) =      0.005                                               Substrate Radius (m) =    0.150                                               Anode Rad.-Virtual Cathode Rad. (m) =                                                                   0.020                                               Deposition Rate (micron/sec) =                                                                          3.000                                               At B = .25 Tesla:                                                             Approx. Substrate Temperature (°K.) =                                                            1569.190                                            Voltage =                 71.938                                              Current =                 820.870                                             Power (kw) =              59.052                                              Thermal Efficiency =      0.575                                               Power Loss to Cathode =   3.530                                               Power Loss to Anode =     6.299                                               Volume Power Losses =     15.25                                               Mass Flow Rate (mgm/sec), Silicon =                                                                     491.973                                             Mass Flow rate (mgm/sec), Hydrogen =                                                                    70.627                                              Mass Flow Rate (mgm/sec), Chlorine =                                                                    0.000                                               Power in Spin (kw) =      1.887                                               Power in Axial Velocity (kw) =                                                                          15.097                                              Power in Ionization Energy (kw) =                                                                       16.984                                              Pressure on Substrate (Torr) =                                                                          4.396                                               Minimum Arc Chamber Pressure (Torr) =                                                                   18.332                                              Maximum Arc Chamber Pressure =                                                                          48.357                                              Max. Silicon Partial Press. in Arc Chmbr. =                                                             9.671                                               ______________________________________                                        Performance characteristics of the                                            Magnetoplasmadynamic source (see FIG. 5)                                      ______________________________________                                        Silicon Source Material = Silicon.                                            Anode radius (m) =        0.050                                               Cathode Radius (m) =      0.005                                               Substrate Radius (m) =    0.150                                               Anode Rad.-Virtual Cathode Rad. (m) =                                                                   0.020                                               Deposition Rate (micron/sec) =                                                                          3.000                                               At B = .25 Tesla:                                                             Approx. Substrate Temperature (°K.) =                                                            1569.190                                            Voltage =                 53.353                                              Current =                 820.870                                             Power (kw) =              43.796                                              Thermal Efficiency =      0.776                                               Power Loss to Cathode =   3.530                                               Power Loss to Anode =     6.299                                               Volume Power losses =     0.000                                               Mass Flow Rates (mgm/sec), Silicon =                                                                    491.973                                             Mass Flow Rates (mgm/sec), Hydrogen =                                                                   0.000                                               Mass Flow Rate (mgm/sec), Chlorine =                                                                    0.000                                               Power in Spin (kw) =      1.887                                               Power in Axial Velocity (kw) =                                                                          15.097                                              Power in Ionization Energy (kw) =                                                                       16.984                                              Pressure on Substrate (Torr) =                                                                          4.396                                               Minimum Arc Chamber Pressure (Torr) =                                                                   17.143                                              Maximum Arc Chamber Pressure =                                                                          20.223                                              Max. Silicon Partial Press. in Arc Chmbr. =                                                             20.223                                              ______________________________________                                    

GENERATION OF THE CONCEPT OF AN ELECTROMAGNETIC THROAT IN ANELECTROMAGNET NOZZLE

Fundamental changes occur in the flow field of a gas when the Machnumber goes from subsonic to supersonic. This is most easilycharacterized by studying the flow of a gas in a channel of varyingcross-section. The expression relating the change in cross sectionalarea of the Mach number is: ##EQU30##

γ=ratio of specific beats

R=gas constant

T=temperature of the gas

A=cross-sectional area of the channel

Three regimes are defined:

M<1 subsonic dA negative

M=1 sonic dA zero

M>1 superxonic dA positive

An equation similar to eq. 45 can be derived for the flow of a singlespecies of charged particles: ##EQU31## where

e=charge of particle

m=mass of particle

u_(cr) ="sonic" velocity of particle

φ=electric potential

Again, three regimes can be defined:

M<1 subsonic edφ negative

M=1 sonic dφ zero

M>1 supersonic edφ positive

The important conclusion to be drawn here is that the electric potentialplays the same role in electromagnetic flow as the channel area does ingas dynamic flow. The electric field must go through a zero in order forthe charged particles to accelerate to a high supersonic velocity. Theposition where this occurs is defined as the electromagnetic throat.

PLASMA PHYSICS AND SCALING CONSIDERATIONS

In deriving 36-46 a number of assumptions about the plasma physics havebeen made. Some of the most relevant are listed below:

a. All of the material injected through the anode is ionized (m=m_(cr)).

b. All of the ionized material in the anode sheath and cathode jet ismagnetically confined within a "magnetic nozzle."

These assumptions have an implicit interaction with regimes of operationthat have been empirically determined, such as size and power level forsteady, efficient operation. An attempt is made in this section to"quantify" some of these empirically determined regimes.

CURRENT CARRYING CAPACITY OF A MAGNETICALLY CONFINED PLASMA

The radial momentum equation for magneto-plasma dynamics has fourdominant terms as follows:

    ∂p/∂r=P (v.sup.2 /r)+jθB.sub.2 -j.sub.2 Bθ

Simply stated, the three terms on the right establish a radial pressuregradient.

(pv² /r) defines a centrifugal force term and contributes a positivegradient to the pressure.

_(j)θ B₂ defines a confining force generated by the plasma diffusingradially outward across the applied magnetic field. The azimuthalcurrent, jθ, is the Hall current generated by this diffusion process.This term contributes a negative pressure gradient.

j_(z) B.sub.θ defines the well-known pinch force term for confining theplasma and contributes a negative pressure gradient.

Some relatively simple modeling can be used in order to obtain aspecific relation among these terms in an axisymmetric cathode jet shownschematically in FIGS. 11, 12 and 16 ##EQU32## In the above equationsthe symbols are defined as follows: ##EQU33## Equations 48 through 51can be introduced into equation 47. The relation that results from thissubstitution is shown below: ##EQU34##

To consistent with the assumptions concerning the radial distribution ofaxial and azimuthal current the radial pressure gradient must be assumedsmall so the the centrifugal force balances the electromagneticconfining forces. This results in the relation: ##EQU35##

The next step is to obtain some relation between the gas density and thecurrent carrying capacity of the column. Since the plasma isapproximately neutral:

    n/=n.sub.c

hence: I=|e|πr_(o) ² n_(e) (w_(l) -w_(e))

Since the current is negative ##EQU36##

Substituting this relation into equation 53 we get: ##EQU37## wherev_(o) =ωr_(o) ##EQU38##

This equation can be written as:

    I.sup.2 -bI+C=0

where ##EQU39##

Both b and c are positive quantities. The solution to this quadraticrelation is: ##EQU40## hence;

    b>I>(b/2)

or

    (b/2)>I>0

and ##EQU41## Consistent with the observation that ##EQU42## thereference current can be written as ##EQU43## In order to obtain theminimum value for the current, the electron axial diffusion velocitymust be made as high as possible. This would be close to "sonic" speed,hence: ##EQU44## The electron temperature should be held below 6000° K.in order to minimize ionization of ambient chlorine or hydrogen atoms.Using the ionization potential for silicon, we get ##EQU45## Using theupper branch of the solution to equation 57 the minimum arc currentshould be between 100 and 200 amperes, depending upon the amount ofdiffusion across the applied magnetic field.

Further insight to this problem may be obtained by considering the casewhen no diffusion occurs across the applied magnetic field lines. Sincespin is induced by the discharge current crossing the applied magneticfield lines, there will be no gas spin, leaving only the pressuregradient to balance the pinch forces. This gives. ##EQU46## Combiningthese relations ##EQU47## Again, if the electron drift velocity w_(e)approaches sonic speed, a minimum useable current can be calculated.This becomes. ##EQU48## when the Mach) number, M, approaches unity. Thetwo expressions for the minimum current will approach each other as

    4 kT.sub.e →|e|V.sub.I

Equation 58 predicts a low current solution exists with the currentrange ##EQU49##

Interesting enough, low current Hall Current Accelerators have beenoperated and results reported, among others, by Hess of NASA Langley andMeyerand of United Aircraft Corp. Typically these devices operate at1-10 amperes of current and voltages of several hundred volts. Theyoperate at low pressure (microns) and some have heated cathodes forelectron sources. Ion production is due to high energy, non-thermalelectrons, hence all species will be ionized to a more or less equalextent.* The mass and energy flux rate are typically two to three ordersof magnitude lower than is available form the high power accelerators,hence they would not provide the desired high deposition rate or powerto maintain the high film temperature. Meyer and observed H³⁰, H₂ ⁺, H₃⁺ in his experiments reported in Ref 14.

The following publications are pertinent to this discussion Hess, R. V.,Experiments and Theory for Continuous Steady Acceleration of Low DensityPlasmas, Proceedings of the XI International Astronautical Congress,Stockholm, Volume I, pp. 404-411 (1960).

Hess, R. V., et al, "Theory and Experiments for the Role of Space-Chargein Plasma Acceleration: in Proceedings of the Symposium onElectromagnetics and Fluid Dynamics of Gaseous Plasma, PolytechnicPress, New York (1961).

R. V. Hess, Experiments and Theory for Continuous Steady Acceleration ofLow Density Plasmas, Proceedings of the XI International AstronauticalCongress, Stockholm 1960. Vol. 1, pp. 404-411. Wien: Springer, 1961.

R. V. Hess, Fundamentals of Plasma Interaction with Electric andMagnetic Fields, Paper No. 59, pp. 313-336, Proceedings of theNASA-University Conference on the Science and Technology of SpaceExploration, Vol. 2, November, 1962.

R. V. Hess, J. Burlock, J. R. Sevier and P. Brockman, Theory andExperiments for the Role of Space-Charge in Plasma Acceleration.Proceedings of the Symposium on Electromagnetics and Fluid Dynamics ofGaseous Plasma, New York, N.Y., April, 1961, pp. 269-307, PolytechnicPress of tee Polytechnic Institute of Brooklyn, 1962.

Meyerand, R. G., Jr. and Brown, S. C., "High-Current 10n Source. "Rev.Sci. Instr., vol., 30, no. 2, February 1959, pp. 110-111.

Meyerand, R. G. Jr., "The Oscillating-Electron Plasma Source." Progressin Astronautics and Rocketry, vol. 5. p. 81 thru 90.

Some reservations must be made concerning the applicability of thegeneral approach adopted here until some critical experiments arecarried out and the results compared with the predictions. Some pointsof concern are as follows:

(i) When electrons are conducting current in an environment dominated bycollisions with atoms and electrons, the drift Mach number is likely tobe much less than unity. This would increase the predicted values forthe minimum current.

(ii) "Classical" diffusion of the plasma across the magnetic field lineshas been assumed. Anomalous diffusion may occur under some operatingconditions, if not in all. This would increase the predicted values forthe minimum current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 8, the magnetoplasmadynamic deposition device 1according to the invention is contained within a vacuum housing 11. Inan upper portion 13 of the magnetoplasmadynamic device 1, is anarc-forming section 15 which is surrounded by accelerating magnet 17.The center portion 21 or the device is located directly beneath thearc-forming section, and is surrounded by a focusing magnet 23. Thelower portion of the device is the deposition chamber 19 which islocated directly beneath the center portion 21, and which contains thedeposition target 53.

In order that some of the ions in the column 25 may be projected intothe deposition chamber 19, it is necessary that a vacuum be maintainedwithin the vacuum housing 11 so that the ions within the plasma column25 are not obstructed by other fluid material between the arc-formingsection 15 and the deposition chamber 19. In the preferred embodiments,a very high vacuum is maintained so that the pressure is below 10⁻⁴Torr. It is preferred to maintain pressure levels of 10⁻⁶ Torr or lowerin order to minimize contamination and extraneous interactions with theworking fluids. However, the economics of decreasing this backgroundpressure must be considered against the cost of increased vacuum pumpingcapacity.

To accomplish these high vacuum levels, a combination of cryosorption,cyrogenic, ionic and mechanical pumping may be used.

FIG. 8 also shows arc section power lead 22, arc section coolingconduits 28, 30 and 32.

Additional extraction of carrier materials is accomplished by a liquidnitrogen-cooled coil assembly 31. The coil assembly 31 is located in thecenter portion 21 so as to surround the column of plasma 25. Gases whichescape from the plasma within the column 25 then condense on the coilassembly 31.

As shown in FIG. 9, the arc-forming section 15 comprises a rod-likecathode 41 and a cylindrical anode 43. An injector 45 is mountedadjacent the cathode so as to permit injected fluid to pass over thecathode 41. When an arc is established between the cathode 41 and anode43, fluid in the vicinity of the arc is ionized, thus forming an ionizedplasma stream.

Referring back to FIG. 7, the fluid ionized in the arc-forming section15 is accelerated by the accelerating magnet set 17 and focused by thefocusing magnet set 23 in order to form the narrow column of plasma 25.However, if the fluid injected by the injector 45 is composed of, orforms elements and compounds of, differing ionization potentials, theelements or compounds with the highest ionization potentials will beunaffected by the discharge and magnetic field and will therefore tendto diffuse out of the column of plasma 25. Furthermore, if binary(molecules), rather than ionic species are formed, these compounds willtend to very rapidly separate themselves from the plasma stream. Thus,such binary compounds may be rapidly extracted. In other words, the ionsformed by injecting fluid with the injector 45 are under the influenceof tile electromagnetic fields formed by the accelerating and focusingmagnets 17, 23, and follow restricted trajectories. Those atoms whichare not under the influence of the electromagnetic field are free todiffuse out of the plasma stream. The different trajectories provide ameans for separating material species.

Because of the different ionization potentials of different materials,the materials can also be separated by ionizing all of the materials.The resulting ions will have different masses and ionization potentialsand will, therefore, have different trajectories as they come under theinfluence of the electromagnetic fields of the accelerating and focusingmagnets 17, 23 and can hence be separated.

As will be described later, in the preferred embodiment, silicontetrachloride will be the primary material injected through the injector45. Elemental silicon becomes separated from the compound in thearc-forming section, thereby leaving chlorine and impurity-containingchlorides. The device must now incorporate some technique of separatingthe chlorine and impurity containing chloride from the silicon whilestill insuring that the partial pressure (of chlorine) within the vacuumhousing 11 remains adequately low (less than 10⁻⁴ Torr). Because of thedifference in the ionization potential between silicon and chlorine, thearc will preferentially ionize the silicon. The silicon ions will betrapped by the applied magnetic fields and the chlorine will diffuse outof the narrow column of ions 25. The coil assembly 31 constitutes theprimary element in a cyrogenic pumping tower. Between the column of ions25 and the coils assembly 31 are cooled baffles 51 which serve tointercept much of the hot, but non-ionized, material which is notconfined in the plasma beam by the magnetic fields and hence tends todiffuse outward. Disassociated atoms which impinge on the cooled bafflewill reassociate to molecules with a corresponding release of energy.The baffles 51 remove this thermal load via external cooling circuitsand hence greatly reduce the thermal load on the cryogenic coil.

When the narrow beam of plasma 25 enters the deposition chamber, ionsremaining in the narrow beam of ions deposit upon a target 53, thusforming a layer or a semiconductor device. Since it is desired thatultimately the semiconductor materials be used outside the device 1, thesemiconductor materials, such as the silicon should be removable fromthe target area. There are several methods of accomplishing this:

(1) A semi-permanent or temporary layer of a material to which thesilicon does not adhere may be placed over the target area. An exampleof this type of material would be boron nitrite. Depending upon theinterface temperature, the boron nitrite will decompose to some extentand the boron will diffuse into the silicon film deposited on the boronnitrite. This results in heavy doping which renders the bottom surfaceof the silicon conducting (approximately=10⁻³ ohms/cm). This permits thebottom surface to act as a back conductor for a semiconductor devicewhich will be formed from the semiconductor material.

(2) The silicon can be deposited on a reusable substrate sheet of arefractory material such as molybdenum or tungsten. By properlycontrolling the thermal cycling of the the substrate, the silicondeposited thereon can be made to break loose from the refractory sheetdue to the difference in the thermal expansion coefficients of the twomaterials.

(3) The silicon call be deposited on the surface of a "pool" of highdensity, low vapor pressure liquid metal such as tin.

(4) The silicon can be deposited upon the surface of a semiconductorbase material, which forms part of the intended semiconductor device.Where the silicon is deposited on solid material (as in cases 1 and 2),it may be desirable to scribe the target materials with grooves in orderto facilitate directional growth of metallic crystals which aredeposited on the target materials. These grooves could be 5-19 micronsdeep, 5-10 microns wide and have a center-to-center separation of 10-15microns between adjacent grooves. This will encourage crystallinenucleation centers formed during thee deposition of the silicon toalign, thereby producing large crystals or even a single crystallinefilm.

DOPANT INJECTION

It is possible to inject a dopant material into the plasma stream inorder to provide a doped layer on the semiconductor material whilecontrolling the depth and density of the doped layer. This is done byinjecting a dopant stimultaneously with the primary semiconductormaterial, either in the same injection port or separately. Thus, as thesemiconductor ions are deposited, the dopant, which is placed in thenarrow column of plasma 25, diffuses into the silicon when the siliconis deposited onto a target 53.

Preferably, the dopant is provided as a gaseous chloride or hydride,acid the chloride or hydride is mixed with the main feed of the siliconcompound in proper proportions just prior to injection into thearc-forming section 15 to the injector 45. Possible compounds could be:

B₂ H₆

PCl₂

PCl₃

AsCl₃

Of these compounds, BCl₃ and PH₃ are considered to be the preferredcompounds for producing silicon solar cells.

Also, as mentioned before, when silicon is deposited on a sheet of boronnitrite, boron doping or the silicon will occur, especially near theinterface between the silicon and the boron nitrite. The temperatures ofthe substrate and of the film will determine the concentration andpenetration of the boron into the silicon.

The following table lists the physical properties of the variousmaterials injected by the system. Ideally, the material injected shouldbe in a fluid or gaseous form. The ionization potential of thoseelements which are to be deposited should be relatively low and theionization potential of carrier materials should be relatively high. Themelting and boiling points of the materials are important for thepurposes of extracting the materials from the environment by passingcryogenic materials through the coil assembly 31.

    __________________________________________________________________________                             Chloride         Vapor                                                  Ionization                                                                          and/or           Pressure (Torr)                     Symbol                                                                             Material Mol. Wt.                                                                           Potential                                                                           Hydride                                                                            M.P.C*                                                                              B.P.C*                                                                              195.8° C.                    __________________________________________________________________________    Si   Silicon  28.06                                                                               8.12      1420  N/A                                       Cl   Chlorine 35.46                                                                              12.95 CL.sub.2                                                                           -101.6                                                                              -34.7 10.sup.-9                           H    Hydrogen 1.00 13.53 H.sub.2                                                                            -259.14                                                                             -252.8                                                                              10.sup.3                            N    Nitrogen 14.01                                                                              14.48 N.sub.2                                                                            -209.86                                                                             -195.8                                                                              760                                      Hydrogen 36.46                                                                              N/A   H Cl -112  -83.7 1.5 × 10.sup.-5                    Chloride                                                                 Preferred Substances                                                          1.   Tetrachlorosilane                                                                      168.29                                                                             N/A   Si Cl.sub.4                                                                        -70   57.57 N/A                                 2.   Trichlorosilane                                                                        135.44                                                                             N/A   Si HCl.sub.3                                                                       -134  33.   N/A                                 3.   Dichlorosilane                                                                         100.99                                                                             N/A   Si H.sub.2 Cl.sub.2                                                                -112  8.3   N/A                                 4.   Chlorosilane                                                                           66.54                                                                              N/A   Si H.sub.3 CL                                                                      -118.1                                                                              -30.4 N/A                                 5.   Silane   32.09                                                                              N/A   Si H.sub.4                                                                         -185  -111.8                                                                              N/A                                 6.   Disilane 62.17                                                                              N/A   Si.sub.2 H.sub.6                                                                   -132.5                                                                              -14.5 N/A                                 7.   Trisilane                                                                              92.24                                                                              N/A   Si.sub.3 H.sub.8                                                                   -177.4                                                                              52.9  N/A                                 8.   Tetrasilane                                                                            122.32                                                                             N/A   Si.sub.4 H.sub.10                                                                  -93.5 80    N/A                                 __________________________________________________________________________

PROCESS AUTOMATION CONSIDERATIONS

In order to produce many square meters of semiconductor grade siliconfilm with one vacuum pump-down operation, some method of moving thesubstrate and/or the target material must be devised. In the embodimentin which a solid substrate is used for a target area, solar cell filmswhich are deposited on the target 53 would be removed from the target 53and stored within the vacuum housing 11, thereby allowing subsequentfilms to be deposited at the target 53.

A robot 55 would be used to lift the subsequent films from the target53. A plurality of completed films 54 are then stored by the robot 55 inthe deposition chamber 19 awas from the target 55 and the plasma column25. It can be seen that this storage of completed films 56 permits thedevice 1 to continue to deposit subsequent films.

It is also possible to have the robot 55 place preformed substrates (notshown) on the target 53 prior to the deposition of each film by thedevice. Thus the completed films 57 would each have their own substrateswhich may be left with the films or later separated from the films.

In the case where the silicon is deposited on the surface of the liquidmetal, the robot 55 may be used to pull the film along the surface ofthe liquid. The film may be continuously deposited and a cutting meanssuch as a laser (not shown) may be used to sever the film into desiredlengths before the lengths are stored as completed films 57.

It is contemplated that the magnetoplasmadynamic deposition device 1 maybe further used to deposited top and bottom conductors and terminals onthe solar cells or conductors. This can be done by suitable dopant aswell as by electrodepositing appropriate metals to the film. Forexample, aluminum may be injected into the arc-forming section 15 in theform of aluminum trichloride. The chloride diffuses from the aluminumand the aluminum ions are projected downward in a narrow column ofplasma 25. This relatively pure aluminum will then form a bond with thesilicon to form a conductor or terminal. A pre-formed grid may be placedon the film in order to enhance the top conductor or terminal. The gridwork is then bonded to the film by the deposition of materials such asaluminum or highly doped silicon. Thus, the completed films 57 wouldhave affixed to them terminals or conductors prior to the removal of thecompleted films from the vacuum housing 11.

Solar cells need anti-reflective coatings in order to improve theircollection of solar power and hence the efficiency of the cell. Thislayer can ideally be made of glass (SiO₂), formed by depositing siliconon top of the top conductor while injecting oxygen over the surface ofthe depositing layer. By proper thermal control of the film during thisdeposition phase, the reaction to form an amorphous glass layer or acrystal quartz layer can be encouraged. The deposition of the siliconand oxygen may be made sequentially in any desired order orsimultaneously.

OPERATION

Referring to FIG. 10, the processes of refining silicon and depositingsolar cells are achieved by carefully controlling the differentmaterials that are injected into the system, as well as the arc controland plasma focusing parameters. Pressure from a pressure control 61 isapplied to a source of silicon tetrachloride 63. The silicontetrachloride is injected into the arc-forming section 15 by means of avaporizer and now controller apparatus 65. One or more dopant supplies71, 73 provide dopant through a dopant control apparatus 75. Hydrogenfrom a hydrogen source 77 may be injected in order to provide additionalcarrier gas to remove impurities and to facilitate the formation ofplasma beam. The various gases formed in the arc-forming section 15 arepumped out at a vacuum pumping section 79. The ions emitted from thearc-forming section 15 are preferentially ionized in order to directsilicon and other materials to be deposited at the target 53 (FIG. 8) ina step represented by block 81. This is achieved by the out-gassingperformed by the vacuum pumping section 79, as well as the focusingmagnets 23. The focusing magnets direct the ions toward the target 53 inthe deposition chamber 19, as represented by step 83. In step 85, thesubstrate is prepared to accept the column of ions 25. This stepincludes the thermal processing of the substrate in order to establishthe substrate at a proper temperature to either adhere or graduallyseparate from the deposited materials, as desired. This is representedas a part of the processing or the substrate by block 87. The ions, asthey impinge upon the target, form a crystalline film, represented by astep 89. The hydrogen provided at 77 may be used to form a plasma beamin order to thermally process the silicon and to prepare the silicon toreceive a dopant layer. This is represented by block 91.

The dopant is then applied, as represented by block 93, after whichfront surface conductors are deposited, using a matrix shield in a steprepresented by block 94.

Final processing is performed at block 95. This processing may includethe deposition of a thin arsenic layer in order to improve thephotosensitive characteristics of the resultant photocells. Finally, instep 96, after the last silicon films or solar cells are formed, thecompleted films or cells 57 are removed from the deposition chamber 19.

ARTICULATING MAGNETS

If it is desired to create large area film substrates, it is necessaryto articulate the target 53 with respect to the narrow column of plasma25. This articulation provides a larger deposition pattern on the target53 than would be achieved by merely permitting the column of plasma 25to diffuse.

As previously mentioned, in the case in which the narrow column ofplasma 25 is focused onto a liquid metal substrate, the robot 55 may beused to pull the deposited materials along the "lake" of liquid metal,thus effectively removing the target 53 relative to the narrow column ofplasma 25.

However, when a solid substrate is used, it is necessary to either movethe target 53 or the column of plasma 25. If it is desired that thetarget 53 be retained in a specific location, then the narrow column ofplasma 25 may be articulated by shifting the magnetic fields of thefocusing magnet 23. This can be achieved by providing an articulatingportion 97 of the focusing magnet 23. The articulating portion 97functions as a part of the focusing magnet 23 but is capable of shiftingits magnetic axis or of shifting its flux pattern in order to angularlydivert the narrow beam of plasma 25 as the plasma approaches the target53. This may be done by selectively energizing part of the articulatingportion 97 or by physically rotating the portion 97 on a gimbalapparatus.

Referring now to FIGS. 11-13, a preferred embodiment of a highthroughput magnetoplasmadynamic processor 100 is disclosed. Theprocessor includes a thermionic cathode 101 surrounded by an insulator103. A buffer electrode 105 is mounted in surrounding relation toinsulator 103, and has extending therethrough a gas inlet conduit 107which communicates with a cavity 109 formed within the electrode 105through helical passages 107'. Cavity 109 has an outlet orifice 111defined by an annular lip 113 which orifice 111 acts to control thepressure of gas within the cavity 109 as well as to assist inestablishing the diameter of cathode jet 115. By controlling thepressure of gas within the cavity 109, the orifice 111 also ensuresstable arc attachment on the conical tip 117 of the cathode 101 whichensures that sufficient gas is ionized to establish the current carryingmagnetically contained cathode jet 115. The above-described structure issealed within a vacuum chamber 119 which has an area designated byreference numeral 121 which sealingly admits therewithin the variouspower, gas and cooling feed-thru lines required for device operation. Asshown in FIGS. 11 and 12, connections 134, 136, 138 are provided forconnection to mechanical vacuum pumps (not shown).

FIG. 28 shows a detailed view of the cathode-buffer 101, 105. As bestshown therein, the straight gas passages 107 extend from the helicalpassages 107' completely through the insulation 103 to a point (notshown) upstream of the cathode 101 at the gas supply. Tubes 102 aremounted in surrounding relation to cathode 101 and convey coolanttherethrough to keep the cathode 101 within desired limits oftemperature. Further, tubes 104 surround buffer 105 and also conveycoolant to keep the buffer 105 within desired temperature limits.

The above-described assemblage of components is placed on the centerlineof a substantially symmetrical electromagnetic coil 123 which centerlinecorresponds to the centerline of the magnetic field produced by the coil123. The coil 123 is specifically designed to give the desired magneticfield strength at the cathode tip 117, in the range of about 0.2 to over10 Tesia, with the peak field strength slightly behind the tip 117 asindicated by line 123A, which ensures a slow divergence of the magneticfield lines downstream of the cathode tip 117. While the coil 123 isshown as located outside the vacuum chamber 119, if desired, it may belocated within vacuum chamber 119.

This design, as above-described, permits the arc cathode attachments tobe as small as 2 millimeters in diameter, even though hundreds ofamperes of current are drawn. Current densities can thus be over 10,000amps/sq. cm. One feature of this type of cathode is that the dischargeis self-sustaining as contrasted to the non-self-sustaining structureof, for example, Tsuchiomoto (U.S. Pat. No. 3,916,034). The (1) heattransfer and (2) ion bombardment to the cathode attachment from theionized gas supply the energy necessary to maintain the temperature oftip 117 near the melting point of tungsten as well as to supply theenergy to "boil" off the electrons, i.e., work function energy, of about4.5 electron volts per electron. The buffered design of cathodediscussed here is essential to obtain the required current capacity andsmall cathode attachment diameter needed for the successful operation ofthe magnetoplasmadynamic processor.

The gas is injected through conduit 107' with as high a swirl componentas is feasible. This accomplishes many objectives, the two mostimportant being:

(1) the arc is thus stabilized on the center line, and

(2) any unionized gas escaping the orifice 111 has a large radialcomponent in velocity and hence will quickly escape from the cathode jetand be pumped out of the vacuum chamber.

Just downstream of the orifice 111, a series of disc-like members 125a-iare mounted within the chamber 119. As is best seen in FIG. 12, thediscs 125a-i preferably have similar outer diameters but their innerdiameters vary, from a small inner diameter for disc 125a progressivelyincreasing to the largest inner diameter for disc 125i. The disc 125i islocated just upstream of the anode 127. The combination of discs 125a-iconstitutes a vacuum insulator/isolator 125. In the region between theorifice 111 and the anode 127, the electric potential lines tend tofollow magnetic field lines whenever plasma exists. The isolator discs125a-i quench any plasma, e.g., plasma streaming back from the anode 127that might form along magnetic field lines between the anode 127 andupstream components such as orifice 111 and the outside cathode set 115,thus permitting a strong radial electric field to develop between inneranode ring 129 and the virtual cathode or cathode jet 115 and also alarge potential difference to develop between the anode 127 and thebuffer electrode 105.

As best seen in FIGS. 12 and 13, anode 127 includes an inner ring 129and an outer cylinder 131 in surrounding relation to ring 129. Cylinder131 has one end 133 formed substantially flush with an end 135 of ring129 and gas another end 137 extending significantly farther downstreamthan end 139 of ring 129, for a purpose to be described hereinafter. Atube 141 is also provided which extends tangentially (see FIG. 13) intoa gap 143 formed between the ring 192 and cylinder. The tube 141conducts feed gas into the gap 143. As shown, the tube 141 is surroundedby a tubing vacuum insulator/isolator structure 145 which includes aninsulator covering 147 made, preferably, of boron nitride, shieldingcylinders 149 of small diameter, shielding cylinders 151 of largediameter and discs 154 of insulator material which fixedly mount (hecylinders 149, 151 to the covering 147. The structure 145 is provided soas to avoid interference between the power lead for anode 127 and thepotential distribution within the vacuum chamber 119. Also best shown inFIGS. 12 and 13, is structure facilitating supply of dopant gas to gap143. The elements of this structure are identical to those related tothe feed gas tube 141 (with one exception) and have been given the samereference numerals with a suffix letter "a." The sole exception lies inthe fact that dopant gas supply structure does not include a power leadeither integral with tube 141a or otherwise, However, if desired, theanode power lead could be incorporated in the dopant gas supplystructure rather than in the feed gas supply structure. As shown, thetube 141 is made of a metallic material and performs two functions: (1)supplies working fluid to gap 143 and (2) comprises the anode powerlead. If desired, however, the power lead could comprise a separateelement if the tube is an insulator. Such separate power lead could bemade concentric with tube 141 if desired. The cylinders 149, 151 arepreferably made of the same material as the working fluid to avoidevaporative contamination in chamber 119. Alternatively, the cylinders149, 151 may be made of a material having low vapor pressure and highmelting point such as, for example, tungsten or molybdenum. If desired,more than two gas inlets 141b, c may be provided to supply gastangentially to gap 143.

The anode 127 and related structure described above are mounted withinthe vacuum chamber 119 and are mounted therein within an ionizing magnetcoil 153 which is used to "fine tune" the magnetic field lines as theypass through the ring 120 and cylinder 131. This fine tuning is done inorder to ensure anode attachment on the lip 155 of ring 129 and so as toobtain the best ionizing efficiency in the gap 157 defined by magneticfield line 159 and cylinder 131.

By injecting the gas with a high azimuthal velocity into the annulus 143the residence time of the gas in the anode is greatly increased overthat which would occur with radial injection, giving a much higherprobability of atom ionization by the part of the annular or rotatingcolumn discharge (anode sheath 159) inside of the outer anode cylinder131.

The correct amount of gas must be injected through the anode to insurethat the desired mode of operation is achieved. By controlling theamount of gas injected, the following modes of operation may beachieved:

(i) single ionization of only one species

(ii) single ionization of more than one species

(iii) multiple ionization of only one species

(iv) multiple ionization of more than one species

(v) erosion of anode material if desired

(vi) ionization and entrainment of ambient gas if desired

(vii) inject gas into anode which will react with anode material to formgaseous compound which is then decomposed by the discharge and the anodematerial ionized.

This is accomplished by reference to equations 36 and 38.

FIG. 29 shows an embodiment of gas supply systems. As shown, the cathodeand buffer 101, 105 are supplied with gas from one of two sources 171,173. A selector valve 175 is switchable between the two sources 171, 173depending upon whether the processor is in the starting or running mode.Valve 175 connects with flow line 177 which includes metering valve 179,restriction 181 and upstream 183 and downstream 185 pressure gaugeswhich enable the gas flow rate to be determined. The flow line 177connects with cathode/buffer gas passages 107.

The anode 127 is fed with dopant gas at gap 143 through tube 141a whichconnects with dopant gas source 170. Also in tube 141a are meteringvalve 172, restriction 174 and pressure gauges 176, 178 which enabledopant gas flow rate to be determined. Feed gas is fed to the gap 143through the above-described tube 141 from feed gas source 180. Tube 141includes metering valve 182, restriction 184 and gauges 186, 188 whichenable feed gas flow rate to be determined.

Also shown in FIG. 29 is a cooling system for tube 141 which includes acoil 190 surrounding tube cover 147. Cooling gas source 191 connects tocoil 190 through tube 192 which also includes connected therein meteringvalve 193, restriction 194 and gauges 195, 196 which enable the flowrate of cooling gas to be determined. Tube 197 connects with thedownstream side of coil 190 and connects with heat exchanger 198 whichacts to remove heat from the cooling gas. Further, to cool the anode127, a line 192a is tapped off coolant line 192 which connects withcooling coil 190a mounted in surrounding relation to anode 127. Theoutlet of coil 190a connects with tube 197 through line 197a.

Referring now, in particular, to FIG. 11, downstream of the anode 127and coil 153 are located a plurality of conical segments 161a-p which asa whole comprise a downstream vacuum insulator/isolator 161, placed at aradius so as not to interfere with the free development of the dischargepath through the anode sheath 159. A group of shaping magnets 163a-f areplaced in surrounding relation to the axis of the plasma beam andsegments 16la-p to control the diameter of the plasma beam that emergesfrom the discharge as well as the direction of the plasma beam.

The object of this downstream isolator array 161 is to intersect allmagnetic field lines that pass through the anode 127 other than thosepassing through the anode orifice 114 and to quench any plasma in theannular region between the isolators 16la-p and the downstreamstructure, e.g., the vacuum tank.

By using three sets of isolator segments (125a-i), (149, 151) and(161a-p) all possible plasma electrical shorting paths betweenstructural components, for example the vacuum tank and the anode,between the vacuum tank and the buffer electrode, and between the anodeand the buffer electrode, are blocked, except for the magnetic fluxlines going through the anode orifice. If no target or substrate isplaced in the path of the beam there is a plasma "electrical short"between the cathode and the tank so that the potential of the tank maystabilize at a level close to that of the cathode.

In actual fact, the axial electric field in the cathode jet reversesdownstream of the region where the cathode jet and anode sheath meet. Atthis position the potential may be 6-15 volts positive with respect tothe cathode. As the electron temperature and density decrease downstreamfrom this region, the potential of the plasma decreases and approachesthat of the cathode. In some cases the plasma potential at the beam tankinterface may be negative with respect to the cathode because of thisplasma potential drop which can be expressed as: ##EQU50## Where theaxial position at which the axial electric field reverses can be definedas an electromagnetic throat in the electromagnetic nozzle. The flow atthis point has a strong similarity to the Mach one condition in regulargas dynamic flow. A detailed analysis of collision less plasma flowindicates that the electric field in the axial direction of flow mustreverse at tile position where each species of particles goes through anequivalent "Mach one" condition. Magnetic field contouring in thedownstream region is required to help establish this "electromagneticthroat" at the desired axial position to accomplish the objectives ofthe processor. As pointed out earlier, no discharge current flowdownstream of the electromagnetic throat. Recirculating currents in allthree directions aximuthal, axial and radial, may flow in this region toestablish the proper condition for the plasma to exit the magneticfield. It is further noted that flow upstream of tile electromagneticthroat is subsonic, whereas flow downstream thereof is supersonic.

At this juncture, it is noted that one of the main points of distinctionbetween the embodiment of FIGS. 11-13 and the embodiment of FIGS. and 9lies in the fact that the processor 100 of FIGS. 1-13 has 3 sets ofmagnets 123, 153 and 163 as opposed to the two sets of magnets 17,23shown in the processor 1. A discussion of the three magnet systemsfollows:

The electromagnetic system provides a number of interrelated functionsin the Hall Current, MPD Accelerator. Primarily, the applied axialmagnetic field provides confinement and direction to the ion flow.Interaction with the current flow also induces a desirably high spinrate of the anode attachment point. The applied magnetic field strengthis one of the three primary parameters which may be varied to exercisecontrol of the MPD operating characteristics. The other two are currentand mass flow rate.

In the deposition process, the downstream magnetic field strength willbe instrumental in the control of the dimensions and uniform depositionrate of silicon particles on the substrate.

For the purpose of design concept discussions, the electromagnets willbe considered in three parts. These are the cathode region acceleratingfield coils, the anode region trimmer coils and the downstream beamconfinement and focusing coils.

ACCELERATING ELECTROMAGNETS

The applied magnetic field in the electrode region should be axial, withmaximum centerline strength slightly aft (away from the anode) of thecathode emitting surface. The resultant magnetic confinement pressurethen gradually decreasing as the electrons flow downstream as thecathode jet, through the anode bore. The desired configuration of themagnetic flux lines are illustrated in FIG. 12 the center plane of theelectromagnets, and the corresponding peak field, are positioned so asto have the cathode tip in a slightly diverging field.

The magnitude of the centerline field strength will be on the order of2,000-20,000 gauss. This presents no technical problem, as such fieldstrengths are easily obtained by fairly compact coils for the innervolume being considered. The minimum size and electrical powerrequirements could be achieved by placing the coils intermittentlyaround the electrode system. For the high vacuum requirements and puritydesired for the deposition process, however, other factors must beconsidered.

SOLENOIDAL ELECTROMAGNET DESIGN

The first examination given to means of obtaining a desirable magneticfield could include the possible usage of permanent magnets as well aselectromagnet varities. However, for the MPD device permanent magnetshave severe limitations. Foremost, little control of the field strengthcan be conveniently obtained. The inherent bulkiness, mass, andsensitivity to thermal and magnetic cycling are undesirable. Further,their field strength deteriorates rapidly above a few hundred degrees.The design concept for the MPD deposition system then will be confinedto electromagnets for the accelerating trimming and focusing fields.

The preliminary design of accelerating magnets can be approached byselection of certain desired quantities, such as centerline fieldstrength, shape of field, method of construction, method of cooling andcritical dimensions. The power input, cooling mass flow rates, forcesand other dimensions can then be calculated.

Three general categories of solenoidal electromagnets can be considered.There are the uniform current density, Bitter and Gaume types (UCD). TheUCD type is typically wound in several layers of square conductor,insulated between and offers great flexibility of design. The Bittercoil is constructed of uniform thickness disks, split radially andjoined to adjacent disks to form a helix. The current density variesinversely as the conductor radius, which improves the center fieldefficiency The Gaume design (FIGS. 25-26) uses disk thickness whichdecrease toward the coil mid-point, and results in both axial and radialcurrent density variation which further increases the efficiency.

In the processor embodiments of this application, the Gaume design hasbeen employed.

In order to obtain adequate control of the strength and shape of themagnetic field in the anode and cathode regions when the electromagnetsare exterior to the vacuum chamber, a trimmer magnet 153 will berequired. It will also be desirable to increase the diameter of thevacuum chamber in at least 3 steps as shown in FIG. 11 in order to getthe coils as close to the centerline as is feasible. The trimmerelectromagnet 153 together with the electromagnet 123 over thecathode-buffer constitute the "acceleration" electromagnets. The coil123 establishes the desired magnetic field strength at the cathode tip(2,000-20,000 gauss) and ensures that the cathode tip is in a magneticfield that diverges downstream. Coil 153 ensures that the field lineswhich pass thru the anode attachment annular ring 129 pass inside of theorifice of the anode cylinder 131 with a gap optimized at between 0.010and 0.100 inches. The induced solenoidal magnetic field from the Hallcurrents in the plasma will affect the shape of this field line and thecurrent through the trimmer 153 magnet must be adjusted to ensure thatthis critical magnetic field line has the proper shape at all operatingconditions. The necessary information on how to adjust this current canbe obtained from the analysis presented along with equations 22-34.

MAGNETIC CONFINEMENT AND FOCUSING

Confinement of the charged particles downstream from the electroderegion is accomplished by an independent electromagnet assembly 163which permits control and shaping of the plasma beam and depositiongeometry. The desired magnetic field profile is such that the ions inthe beam will be confined and directed entirely onto the substrate,while the non-ionized carrier gases and contaminates will diffuse fromthe beam and be captured on the cryogenic surfaces or by other pumpingmechanisms.

The basis for this magnetic separation of silicon from the othermaterials, as discussed earlier, lies in the tendency of the arc tooperate with a minimum potential drop. This strongly favors theionization of silicon which has an ionization potential of about 8electron volts as compared with about 13 volts for either hydrogen orchlorine.

This confinement of the silicon ions and focusing onto the substratearea can be accomplished with a slowly divergent magnetic field, downthe length of the anode-to-substrate axis. This field must blendproperly with the higher field produced by the accelerating coils, andsmoothly decrease in strength along the axis to the substrate.

The overall magnetic flux line contours for the device are idealized inFIG. 11. The flux lines which intersect the anode bore diameter, wherethe working fluid is injected into the plasma and subsequently ionized,should also intersect the outer diameter of the substrate. The ionstherein will be accelerated axially and radially due to the electricfields and the applied axial magnetic field will deflect the radial ionmotion into azimuthal motion.

The resultant ion flow towards the substrate will generally be confinedwithin the region bounded by the anode bore to substrate O.D. flux lines166, with substantial inward ion movement, radially toward the cathodejet region to produce a fairly uniform radial distribution of mass atthe substrate surface. Reference numeral 168 (FIG. 12) refers to linesof equal electric potential.

The design of electromagnets to produce a confining field can beapproached on the following basis:

(1) The ion boundary defined by the anode bore to substrate O.D. fluxlines can be established by fixing a constant value of magnetic flux atany axial position, i.e. induction times area will be constant.

    B.sub.2 r.sup.2 =Constant                                  71

    B.sub.2=(r.sub.a /r.sub.z).sup.2 B.sub.o                   72

For preliminary anode values of r_(a) =0.05 meters and B_(a=) O.2 Tesia,the axial field strength at the substrate should be: ##EQU51##

(2) It is desirable to have a fairly uniform magnetic field in theregion of the substrate, and for the field to be predominatly axial,with minimum radial components, all for the purpose of uniform siliconion focusing onto the substrate, i.e.

    B.sub.z (r,z=B.sub.z (0.2)                                 73

and

    B.sub.z >>B.sub.r

(3) the desired profile of the overall field strength (accelerating,trimmering and focussing) is illustrated in FIG. 27, as a convenient wayto present the concept. The maximum field position is slightly behindthe cathode tip, and the field strength decreases smoothly towards thesubstrate, inversely proportional to the bounded area at any point alongthe centerline.

These three criteria can be satisfied by a solenoidal coilconfiguration. It is known that the field inside a long solenoid isfairly uniform across the bore and that it decreases in cosine fashionfrom the midpoint towards the ends. The value at the ends of a very longsolenoid is half that at the midpoint.

FIG. 27 shows, for orientation purposes, the accelerator cathode magnet123, the anode trimmer magnet 153, the downstream focussing magnets 163as well as the cathode 101, anode 127 and insulator/isolators 125, 161.

The typical, symmetrical bell-curve field strength shape of a simplesolenoid would accomplish the task, but the half of the field whichwould exist aft of the cathode, and the power required to generate it,would be entirely wasted. A better approach would be a long solenoid oflower field strength adding to the downstream field of the acceleratingcoil, or by the cumulative effect of a series of short coils which couldbe placed at intervals along the centerline.

Some feeling for the magnitude of this electromagnet can be quicklyderived from simplified calculations:

(1) For a vacuum chamber of 1.5 meters diameter and 3 meters length,assume exterior placement of the confining solenoid.

(2) Consider the case as a solenoid with the substrate at one end andthe electrode array at the other.

The field strength at the substrate then will be about one-half of themidpoint value, or

    B.sub.ss =(μ.sub.o /2)(NI/1)                            74

which was previously determined to have a value of 0.022 Tesia.Therefore, ##EQU52## For comparison, this is approximately twice thevalue required for the accelerating field.

The confining coil design will now be dictated by the requirements forpower supply matching and minimum copper costs. These quantities may berelated as:

    Copper Cost=K.sub.1 l.sub.c A.sub.cs                       75

    Power Required=K.sub.x I.sup.2 (l.sub.c /A.sub.cs)         76

where

l_(c) =length of conductor

A_(cs) =conductor cross-sectional area

K₁ l & K₂ are constant

The length of the conductor when wound on the O.D. of the vacuum chamberwill be:

    l.sub.c =2 r.sub.i N                                       77

and since ##EQU53## Substituting above:

    Copper cost=K.sub.3 (A.sub.cs /I)                          78

    Power Requirements=K.sub.4 (I/A.sub.cs)                    79

The copper costs and power costs are hence inversely related and cannotbe optimized separately. The preliminary design then will be based onthe selection of a convenient power supply voltage, say 400 VDC, withthe conductor sizing and current to be determined. ##EQU54## Earlier,Il_(c) was found to be =33 X 10⁴ amp-m, ##EQU55## For a conservativecurrent of 10 amperes; ##EQU56## For a higher current level of 100 A ormore which would require conductor cooling for continuous usage:

l_(c) =3300 m

m_(cu) =412 Kgm

P=40 Kw

FIG. 14 shows schematically the magnet flux lines generated by passingcurrent through the solenoid coil in the direction indicated by arrows163. It also shows schematically the two niain features of theelectrical discharge:

(i) the central cathode jet 165 or virtual cathode consisting of plasmagenerated by the discharge inside the cathode buffer and augmented byions captured from the anode sheath.

(ii) the annular anode sheath 167 which consists of plasma produced byionizing the material injected through the anode. Moving downstream, theoutside diameter of the anode sheath will encompass less and lessmagnetic flux, φ.

FIG. 15 shows how the radial plasma dynamic forces on the plasma,j.sub.θ B_(z) -j_(z) B.sub.θ, separate the plasma into the structuredescribed in FIG. 14. The axial forces, j_(r) B.sub.θ -j.sub.θ B_(r),accelerate the plasma in the downstream direction, provided thesolenoidal magnetic field diverges. Magnetic field lines of the inducedmagnetic field due to the Hall currents are also shown scbematically.These demonstrate the diamagnetic properties of the plasma, tilat is,the Hall currents flow so as to try and exclude magnetic field linesfrom the volume occupied by the plasma. A great deal can be learned fromexamining the reaction forces on the currents in the magnet and thepower leads. The radial component of the induced solenoidal fieldinteracts with the current through the coil to give a net rearward forceon the magnet. If the anode power lead is radial, the axial component ofthe applied solenoidal magnetic field interacts with the current in thepower lead to generate a torque on the power lead. The azimuthalmagnetic field, interacting with the power lead that radially connectsthe anode and cathode to the power supply, also given a net rearwardforce on the structure comprising the electric circuit. Since "action"must equal "reaction" the plasma leaving the system carries both axialand angular momentum with it, which was imparted to it by theelectromagnetic interactions.

FIG. 16 shows the paths taken by the electric current. This includesinduced Hall currents, as well as the discharge current.

FIGS. 17-19 show schematically the flow paths of all three species ofparticles; atoms, ions and electrons.

The magnetoplasmadynamic plasma processor described hereinabove is by nomeans a "conventional" plasma generator. From the previous sections itcan be seen that great sophistication in technology and an equally deepunderstanding of plasma physics has been required to design andsuccessfully operate this device. Some of the unique design andoperational features are sunimarized below:

(1) The thermionic cathode must be buffered. (2) The orifice diameter inthe buffer, the type and flow rate of the gas through this componentmust all be chosen to match the operational requirements of the device.This gas flow may be inert material (helium or argon), or it may containmaterial relevant to the accomplishment of the objectives of the device,e.g.,

a gas containing dopant materials for a semiconductor material which isinjected through the anode.

It is suggested that, in general, the flow rate through this bufferelectrode is usually less than 1/10th that injected through the anode.

(3) Adequate gas swirl must be established and maintained in this gasflow.

(4) The strength and configuration of the magnetic field near the gascathode tip 117 must be tailored to match the geometry; otherwisecathode-to-buffer sborting and/or unstable cathode attachnient canoccur.

(5) Ttie upstream isolator discs 125a-i niust be very precisely designedand positioned to accomplish the required vacuum electrical insulationbetween the anode and upstream structure.

(6) All plasma upstream of the anode must be electro-magneticallyconfined in the cathode jet, predominantly by pinch forces. The plasmain this region follows magnetic field lines fairly closely. If, however,as the plasma flows downstream it encompasses more magnetic field lines,then an azimuthal velocity will be induced in the plasma. The spindirection of the injected gas must be in the same direction as theelectromagnetically induced spin, e.g., if the axial component of theapplied magnetic field points in the downstream direction form thecahtode tip 117, then the spin direction will be clockwise lookingdownstream.

(7) The anode-ionizer combination 127, etc., is extremely sophisticatedas to shape and functions:

(a) it represents the best compromise between mechanical andelectromagnetic confinement in order to get high mass utilization, i.e.,ionize a high percentage of the material injected thru the anode 125which one wants to ionize in order to accomplish the objectives of theprocessor.

(b) fine-tuning of the solenoidal magnetic field near the anode 127 isrequired to maintain the attachment point of the discharge on thecorrect lip 129.

(c) the gap between the discharge 157 (anode sheath) and the gascontainnient cylinder must be optimized.

(d) the gas spin velocity at injection must be as high as possible.

(e) the correct amount of gas must be injected thru the anode to insurethat the desired mode of operation is achieved, e.g.:

(i) single ionization of only one species

(ii) single ionization of more than one species

(iii) multiple ionization of only one species

(iv) multiple ionization of more than one species

(v) erosion of anode material if desired

(vi) ionization and entrainment of ambient gas if desired

(vii) other

This is acconiplislied by reference to the equation for critical massflow rate ##EQU57##

(8) It is essential that the major component of the working fluid beinjected through the anode 127 through conduit 141, so that the ions,once formed, take up the cycloidal motion illustrated in FIGS. 18 and 23under the combined action of the radial electric and axial magneticfields.

(9) If the magnetic field is made to diverge (even slightly) downstreamof the anode 127, the "oscillating" ions produced in the anode sheathwill be eletromagnetically accelerated axially and move slowlydownstream. The magnetic field must be contoured to achieve the desireddownstream velocity of these ions. As the ions move radially andazimuthally, they pass through the outer layer of the cathode jet, whichconsists initially only of cold ions (ionized material from thecathode-buffer). Elastic collision can occur between the oscillatingions and the ions and electrons in the cathode jet. Elastic collisionsbetween the oscillating ions and the "cool" cathode jet ions can resultin capture of the oscillating ions inside the cathode jet. Conservationof angular niomentum requires that the spin velocity of the material inthe cathode jet increase as more oscillating ions are captured. Thisrate of transfer of ions from the anode sheath to cathode jet representsa flow of electric current. This "ion current" can carry a significantfraction of the total discharge current between the anode sheath and thecathode jet; however, enough electron current must cross from thecathode jet over to the anode sheath to supply the high energy electronsneeded to ionize the atoms of working fluid in the anode region andextended anode sheath.

(10) Downstream of the "electromagnetic throat" the plasma flow path 169is determined by the magnetic field strength and shape and the plasmavelocity. This is, however, not a conventional thermal plasma, where theenergy resides primarily in the thermal motion as defined by atemperature. Typical plasma temperatures are 6000° K. to 40,000° K. Theplasma that exits from the electromagnetic throat has the followingcharacteristics:

(a) The ions and electrons have a high spin velocity and a comparableaxial velocity.

(b) The ion temperature is less than 4000° K.

(c) The electron temperature may be anywhere between 6000° K. and100,000° K. immediately downstrcain of the electromagnetic throat.

(d) The electron pressure will be high at the electromagnetic throat andthe electrons will try to expand axially downstream. In doing so theyset up an electric field which accelerates the ions. In this way theelectron internal energy is transferred into axial kinetic energy on theions. Also, if the diameter of the plasma beam expands, i.e., themagnetic field diverges, rotational ion energy transfers over to axialion energy in order to converve angular momentum. Hence by a properchoice of the target position and of the magtictic field contour one cancontrol at the target:

(i) the electron temperature

(ii) the axial ion velocity

(iii) the azimuthal ion velocity

(iv) the beam cross-sectional area and hence

(v) the mass flux density, the momentum flux density and the heat fluxdensity.

This is the only plasma device known to the inventor that permits suchprecise control of the total particle energy as well as of mass,momentum and energy flux rates at a target or substrate surface.

(11) The distance between the anode-ionizer office 158 and thepositioning where the current terminates (electromagnetic throat 144) isgiven approximately by: ##EQU58## where φ=πR_(A) ² (B_(z))_(A)

R_(A) =inner radius of anode.

(B_(z))_(A) =average strength of the axial magnetic field at the anode.

σ=electrical conductivity of the gas in the cathode jet.

k=Boltzman's constant

T=Gas (electron) temperature

m=mass flow rate in the cathode jet.

m_(a) =mass of atome of gas flowing in the cathode jet.

I=current flowing thru the cathode jet.

e=charge in the electron. ##EQU59## Typical values for the abovequantities could be: ##EQU60## If the magnetic field were increased from1000 gauss to 2000 gauss, the distance L would increase to 106 inches.

The following table defines the axial, radial and tangential forcesgenerated in the inventive device.

                  TABLE 4                                                         ______________________________________                                        Radial Forces:                                                                (1) B.sub.z j.sub.θ                                                                 These forces result in pressures which serve                                  to confine the jet to a narrow beam and,                                      by reaction against the electrodes, to pro-                                   duce useful thrust.                                               (2) B.sub.θ j.sub.z                                                     Tangential Forces:                                                            (1) B.sub.z j.sub.r                                                                       These forces induce the azimuthal Hall                                        currents.                                                         (2) B.sub.r j.sub.z                                                           Axial Forces:                                                                 (1) B.sub.θ j.sub.r                                                                 This is the self-magnetic field                                               pumping force.                                                    (2) B.sub.r j.sub.θ                                                                 This force results from the interaction of                                    the Hall currents with the magnetic nozzle.                                   Both axial forces serve to accelerate the plasma.                 ______________________________________                                    

FIG. 24 is a graph showing the film thickness deposited on the processorcollector several meters downstream of the processor as a function ofthe radial position from the center line of the collector. FIG. 24indicates that a fairly uniform film can be deposited over a surfacearea of 60 inches diameter (1.82 square meters).

Table 5 shows data taken from a test of a lithium thruster deviceaccording to the invention.

                                      TABLE 5                                     __________________________________________________________________________                 P.sub.t                                                          Point                                                                            T  m   I.sub.sp                                                                         10.sup.-4                                                                        I.sub.A                                                                          V.sub.A                                                                          P.sub.A                                                                          P.sub.mag                                                                        P.sub.c+b                                                                        P.sub.an                                                                         *  ** ***                                   No.                                                                              gram                                                                             mg/sec                                                                            sec                                                                              torr                                                                             amp                                                                              volt                                                                             kW kW kW kW η.sub.TH                                                                     η.sub.F                                                                      η.sub.o                           __________________________________________________________________________    Run 732 (contd)                                                               85 24.0                                                                             5.68                                                                              4225                                                                             (1.0)                                                                            300                                                                              56.0                                                                             16.80                                                                            3.18                                                                             4.97  0.556                                                                            0.290                                                                            0.244                                 86 24.9                                                                             5.68                                                                              4383                                                                             -- 300                                                                              56.0                                                                             16.80                                                                            3.18                                                                             5.04  0.552                                                                            0.312                                                                            0.262                                 87 25.2                                                                             5.68                                                                              4430                                                                             2.4                                                                              302                                                                              57.0                                                                             17.21                                                                            3.20                                                                             5.00  0.558                                                                            0.312                                                                            0.263                                 88 26.9                                                                             5.66                                                                              4752                                                                             (1.1)                                                                            300                                                                              54.5                                                                             16.35                                                                            3.18                                                                             4.68  0.617                                                                            0.375                                                                            0.314                                 89 31.0                                                                             5.67                                                                              5467                                                                             0.9                                                                              300                                                                              53.5                                                                             16.05                                                                            ↑                                                                          4.57  0.615                                                                            0.507                                                                            0.423                                 90 24.5                                                                             5.67                                                                              4320                                                                             2.1                                                                              300                                                                              56.0                                                                             16.80 5.20  0.548                                                                            0.302                                                                            0.254                                 91 24.3                                                                             5.66                                                                              4293                                                                             2.0                                                                              300                                                                              56.2                                                                             16.86 5.20  0.552                                                                            0.297                                                                            0.250                                 92 24.3                                                                             5.65                                                                              4300                                                                             2.2                                                                              300                                                                              56.3                                                                             16.89 5.30  0.541                                                                            0.297                                                                            0.250                                 93 24.1                                                                             5.65                                                                              4265                                                                             2.1                                                                              302                                                                              56.3                                                                             17.00 5.28  0.547                                                                            0.290                                                                            0.244                                 94 24.8                                                                             5.65                                                                              4389                                                                             2.1                                                                              303                                                                              55.7                                                                             16.88 5.26  0.536                                                                            0.309                                                                            0.260                                 95 23.7                                                                             5.66                                                                              4187                                                                             2.1                                                                              303                                                                              56.0                                                                             16.97                                                                            ↓                                                                         5.19  0.549                                                                            0.281                                                                            0.236                                 96 23.3                                                                             5.66                                                                              4098                                                                             2.1                                                                              303                                                                              54.5                                                                             16.51                                                                            3.18                                                                             5.08  0.545                                                                            0.276                                                                            0.232                                 97 22.8                                                                             5.06                                                                              4028                                                                             2.1                                                                              304                                                                              55.0                                                                             16.72                                                                            3.20                                                                             5.08  0.548                                                                            0.264                                                                            0.221                                 98 22.5                                                                             5.66                                                                              3975                                                                             2.1                                                                              302                                                                              54.5                                                                             16.46                                                                            3.15                                                                             5.08  0.541                                                                            0.261                                                                            0.219                                 99 22.2                                                                             5.65                                                                              3929                                                                             2.0                                                                              302                                                                              55.5                                                                             16.76                                                                            3.15                                                                             5.26  0.537                                                                            0.250                                                                            0.210                                 100                                                                              21.7                                                                             5.65                                                                              3840                                                                             2.0                                                                              303                                                                              55.7                                                                             16.88                                                                            3.15                                                                             5.13  0.548                                                                            0.237                                                                            0.200                                 101                                                                              21.6                                                                             5.65                                                                              3823                                                                             1.9                                                                              303                                                                              55.7                                                                             16.88                                                                            3.18                                                                             5.17  0.547                                                                            0.235                                                                            0.198                                 102                                                                              22.3                                                                             5.65                                                                              3946                                                                             2.0                                                                              303                                                                              56.2                                                                             17.03                                                                            3.15                                                                             5.24  0.546                                                                            0.248                                                                            0.209                                 __________________________________________________________________________     *Thermal efficiency not including magnet power                                **Thrust efficiency not including magnet power                                ***Thrust efficiency not including magnet power                          

In Table 5, the columns of data are defined as follows:

T=thrust in grams

m=mass flow rate in milligrams/sec.

I_(sp) =specific impulse in sec.

P_(t) =chamber pressure

I_(A) =current of the discharge

V_(A) =potential drop across the discharge

P_(A) =electrical power of discharge

P_(mag) =electrical power in the magnets

P_(c+b) =power loss from the cathode and buffer

P_(an) =power loss from the anode

η_(th) =thermal efficiency

η_(f) =thrust efficiency excluding magnet power

η_(o) =thrust efficiency including magnet power

Referring to FIG. 21 where like elements (with respect to FIGS. 11-13)have like primed reference numerals, a further embodiment of plasmaprocessor 200 includes cathode 105' including orifice 111', anode 127'including ring 129' and cylindrical portion 131'. Between the cathode105' and anode 127' are mounted a series of discs 125'a-c which in totocomprise an upstream vacuum insulator/isolator 125'. A single magnet 224is shown surrounding the cathode 105' and anode 127', however, ifdesired, magnets corresponding to the magnets 123, 153 of the FIGS.11-13 embodiment may be employed. Downstream of anode 127' are mountedvacuum insulator/isolator members 161'a-l which comprise a series oftruncated conical members. Surrounding the members 161' are toroidal ionpump cathodes 272 and anodes 274 which are in turn surrounded bytoroidal electromagnets 163'a-f shown mounted outside chamber 119' butmountable therewithin, if desired. The electromagnets 163' perform twofunctions: (1) they confine the plasma beam to a desired configuration,and (2) they act in conjunction with cathodes 272 and anodes 274 to pumpmaterial from the beam 270 which the operator wishes to separate fromthe beam. Reference numeral 250 refers to the substrate where the beam270 is concentrated while 252 and 254 are substrate shields. As shown,conduits 282, 284 and 286 supply coolant to substrate 250 whilecylindrical member 288 comprises a radiation shield for substrate 250.

In operation, this enibodiment is designed specifically for separating 2or more species. The ionization potential of one being significantlylower than that of the others. Further, the species with the lowionization potential must be condensible as a solid on the collector(250). The collector is maintained at a temperature which ensurescondensation and keeps the vapor pressure of this condensate below 10⁻²Torr through appropriate cooling pipes (282) (284) (286) and shield 288.The other component (materials with higher ionization potentials) arepumped from the system using combinations of ion pumps, (163) (272)(274) and mechanical pumps (290, 292, 294, and 296).

To ensure good separation the following conditions must be met:

(1) The mass flow rate of the low ionization potential component must beequal to or slightly greater than the critical mass flow rate for singleionization.

(2) This material must be injected through the anodeionizer (127 whichis designed so that most of the molecules are dissociated and the atomsof this component are ionized inside of the anode-ionizer structure.This is accomplished by inelastic collisions between the molecules andatoms and high energy electrons in the anode sheath (167).

(3) In order to obtain as high a residence time (defined as the timeduring which the atom or molecule remains within the outer cylindricalportion 131') as possible, the material is injected with as high anazimuthal velocity as is possible.

(4) The ionized material will be electromagnetically confined to theplasma beam (270) and pass through the electromagnetic throat.

(5) The parameters of the processor and facility must be chosen toposition this electromagnetic throat (using eq. 85) at the desired axiallocation.

(6) Once the unionized atoms and molecules exit the anode orifice(158'), their angular momentum will send them on radial trajectoriestoward the ion and mechanical pumps thru the downstreamisolator/insulator segments 161'.

(7) These atoms and molecules are removed from the ambient by the ionand mechanical pumps.

(8) The ionized material is deposited on the target/substrate. Thismaterial may be collected in any of the following forms:

(i) bulk material

(ii) thin films of any desired crystallinity, e.g. single crystal,polycrystal, amorphous.

(iii) wafers of any desired crystallinity, e.g. single crystal,polycrystal, amorphous.

(iv) coatings on simple or complicated shapes.

(v) thick films on some dissolvable or otherwise removable substrate soas to form simple or complicated self-supporting structures once thesubstrate is dissolved or removed

In practice, most metals and semiconductors have low ionizationpotentials (5 to 10 electron volts) and gases. e.g. hydrogen, chlorine,nitrogen, etc. have high ionization potentials (12-18 electron volts).The magnetoplasmadynamic processor thus provides a means for separatingmetals from many of their compounds. The major restriction on thecompound is that it must be capable of being fed through the anode influid or gaseous form. The magnetoplasmadynamic processor used in thisimplementation can, in many cases, provide a less expensive and fasteralternative to:

(i) electro-deposition

(ii) vapor deposition.

(iii) chemical vapor deposition.

(iv) production of semiconductor wafers by any existing technique.

The implementation shown in FIG. 21 is best suited to separating metalsor semiconductors from hydrides. An implementation using the cryogenicpumps shown in FIG. 8, rather than the ion pumps of FIG. 21 would bebetter suited for separating metals or semiconductors from halidecompounds. A partial listing of materials that can be fed thru theprocessor as hydrides or chlorides as shown in Table 6. The meltingpoint and boiling point of these compounds are also shown in the Table,indicating that it is feasible to feed the compounds thru the processoras fluids. The first ionization potential of the metallic orsemi-conductor components, as well as those for hydrogen and chlorineare also shown in the table. These values show that significantdifferences exist between the ionization potential of the carriermaterial and that of the material to be deposited, thus permittingseparation by the processor.

When high purity of the deposited material is required as many componentparts of the processor as is feasible should be made from the materialwhich is to be deposited. For instance, if silicon is to be deposited,the anode parts, the buffer electrode and the isolator segments shouldall be fabricated from or coated with pure silicon.

The processor and facility must be designed to obtain the desired mass,energy and momentum flux at the target/substrate. When this is done, thedesired thermal processing of the depositing layer can be achieved; e.g.

(i) self annealing

(ii) inter difrusion of two or more substances.

Partial listing of materials that can be injected as chlorides orhydrides:

                  TABLE 6                                                         ______________________________________                                                                      Metallic Ionization                                     Melting    Boiling    Potential                                       Material                                                                              Point      Point      Component                                       ______________________________________                                        Ga Cl.sub.3                                                                           77.9       201.3      5.999                                           As Cl.sub.3                                                                           -8.5       130.2      9.81                                            Ge Cl.sub.4                                                                           -49.5       84        7.899                                           Mg Cl.sub.2                                                                           714        1412       7.646                                           Mo Cl.sub.5                                                                           194        268        7.099                                           Nb Cl   264.7      254        6.88                                            PA Cl.sub.2                                                                           6.05       d 581      9.0                                             Re Cl.sub.4        500        7.88                                            Si Cl.sub.4                                                                           -70         57.6      8.151                                           Ti Cl.sub.4                                                                           -25        136.4      6.82                                            W Cl.sub.5                                                                            248        275.6      7.98                                            Cl                            12.967                                          B.sub.2 H.sub.6                                                                       -165.5     -92.5      8.298                                           As H.sub.3                                                                            -116.3     -55        9.81                                            Ga.sub.2 H.sub.6                                                                      -21.4      139        5.999                                           Ge H.sub.4                                                                            -165       -88.5      7.899                                           P H.sub.3                                                                             -133       -87.7      10.486                                          Si H.sub.4                                                                            -185       -111.8     8.151                                           H                             13.598                                          ______________________________________                                    

Many materials can be injected thru the processor as vapor, produced ina refractory metal boiler. In this case, the processor components shouldbe fabricated from refractory metal materials or high melting pointmetallic or semi-conductor materials that do no react with the workingfluid, A partial listing of materials than can be fed thru the processorin this manner is shown in Table 7. When the processor is operating inthis mode, the ion and mechanical pumps act to pump any residual gasesor other volatile components from the ambient.

As before, the material can be deposited in any of the following forms.

(i) Bulk material.

(ii) thin films of any desired crystallinity, e.g. single crystal,polycrystal, amorphous.

(iii) wafers of any desired crystallinity, e.g. single crystal,polycrystal, amorphous.

(iv) coatings on simple or complicated shapes.

(v) thick films on some dissolvable or otherwise removable substrate soas to form simple or complicated self-supporting structures once thesubstrate is dissolved or removed.

                  TABLE 7                                                         ______________________________________                                        Partial list of materials that can be injected thru the anode                 as vapor produced in a refractory metal boiler:                               ______________________________________                                        Silver                Phosphorus                                              Arsenic               Lead                                                    Barium                Rubidium                                                Bismuth               Sulfur                                                  Calcium               Antimony                                                Cadmium               Selenium                                                Cesium                Samarium                                                Callium               Strontium                                               Potassium             Tellurium                                               Indium                Thallium                                                Magnesium             Thulium                                                 Manganese             Ytterbium                                               Sodium                Zinc                                                    ______________________________________                                    

Injection techniques similar to that shown in FIG. 13 can be used toinject, simultaneously, two or more materials. These materials shouldbave comparable ionization potentials. Many semi-conductor materials canbe formed in this manner. A partial listing is shown in TABLE 8.

Besides forming semiconductor compounds, many other types of compoundsand/or mixtures can be formed by simultaneous injection of two or moreelements thru the processor and creating the proper thermal environmentat the target or substrate to obtain the desired reaction rates andinter diffusion rates.

Compounds and/or mixtures can also be produced at the target orsubstrate by depositing only one substance and creating the properthermal environment for it to react or mix with the material of thesubstrate.

By properly controlling the beam dianicter, the size and number ofradiation shields around the target, and the flow rate of coolant, theproper thermal environment can be obtained using only the energy flowrate from the depositing beam of plasma.

                  TABLE 8                                                         ______________________________________                                        Partial list of semi conductor compounds or elements that can                 be produced by injection of elements as vapors through the                    ______________________________________                                        processor.                                                                    Amorphous selenium    Se                                                      Grey tin              Sn                                                      Tellurium             Te                                                      Cadmium sulfide       CdS                                                     Cadmium selenide      CdSe                                                    Cadmium telluride     CdTe                                                    Gallium arsenide      GaAr                                                    Lead sulphide         PbS                                                     Lead selenide         PbSe                                                    Lead teluride         PbTe                                                    Zinc sulphide         ZnS                                                     Gallium antimonide    GaSb                                                    Indium arsinide       JnAs                                                    Indium phosphate      InP                                                     Indium antimonide     InSb                                                    ______________________________________                                    

The embodiments described in FIGS. 21-23 include a further feature incommon, namely, they utilize three types of pumping means, mechanical,sorption and ion types to keep the vacuum chambers thereof free ofundesired contamination. These vacuum pumping systems are furtherdescribed as follows:

The type and capacity of vacuum pumping equipment for this inventionwill be dictated primarily by the physical and chemical properties ofthe elements or compounds to be used in the deposition process, theirmass flow rate, and their relative temperatures. The prime candidatesfor deposition feed stock are the hydrogen and chloride compounds ofsilicon, so the separation and pumping schemes must be designed toeffectively remove these from the process stream. The mechanisms andeffectiveness of separation from silicon is treated elsewhere. The mosteffective means for pumping these two gases over and above mechanicalmeans must involve different systems for each, due to their dissimilarproperties.

1.HYDROGEN PUMPING

The mass flow rate of hydrogen that will be involved under variouscircumstances is well known. For vacuum systems design purposes, theinaximuin anticipated quantity may be approximated as follows: Takingthe maximum deposition rate of silicon oil the substrate to be 10⁴ or 1μ/s, the mass flow rate of silicon onto a substrate of 400 area (20cm×20 cm) would be: ##EQU61## Assume that the efficiency of utilizationof the silicon would be 50%, i.e. one-half of the silicon mass wbich isfed through the anode will be effectively deposited onto the substrate.The anode mass flow rate of silicon is then 200 milligram/sec.

For the utilization of silane gas as the feed stock, the mass flow rateswould be: ##EQU62##

The pumping speed required for removal of the hydrogen will bedependent, among other things, upon the desired background pressurelevel to be maintained. Assuming a value of 10⁻⁵ Torr, the volumetricpumping speed would be: ##EQU63##

This represents a very large and expensive pumping facility if typicalion pumps of commercial availability were to be used. Much morerealistic facility requirements can be established by selecting lowerdeposition rates and higher ambient operation pressure levels. Forexample, deposition of 10² Å/sec and operation at 10⁻⁴ Torr would reducethe hydrogen speed demand by three orders of magnitude, or to 20,000liters/sec.

Commercially available pumps, such as the Perkin-Elmer Ultek Hydrogen500 units can handle over 800 liters/second of hydrogen at 10⁻⁴ Torr.The lower values of hydrogen could then be managed with 25 of theseunits. Long term operation at 10⁻⁴ Torr is not recommended, however, andother methods of solution are to be examined. For example, verysignificant advantages could be gained if the hydrogen density wereincreased before ion pumping by lowering the temperature. Stainlesssteel shrouds which are cooled by liquid nitrogen could be used toeffect pumping speed gains roughly in proportion to the ratio of theabsolute hydrogen temperatures at absorption and subsequent evaporationfrom those surfaces. Structure similar to this is shown in theembodiment of FIGS. 8-10

An inherent feature of the MPD device, that might be efficientlyutilized for ion type vacuum pumping, is the axial magnetic confiningfield. This field is nominally about 2000 gauss or 0.2 webers/m², whichcoincides with the typical field strength used in commercial ion pumps.The application of this existing axial magnetic field to ion pumpinginvolves the placement of anode 274 and cathode 272 rings directlyinside the test chamber, stacked alternately along the axis of thechamber. The plates would then intersect the applied axial flux lines,in the same manner as commercial ion pumps, with the noteable advantageof very large cathode collecting surfaces (or noncathode collectingsurfaces in the case of a tripod pump design) and "free" magneticfields. It would seem to be possible by careful design to achieve one totwo orders of magnitude improvement by this method versus the exteriorattachment through ports of a comparatively few commercial ion pumps tothe chamber. This custom ion pump concept is illustrated in FIGS. 21-22.

Alternate methods of pumping include cryogenic and cryosorption. Bothmethods involve collection of the gas on cold surfaces, such as theshroud-like insulator/isolators 161 shown in FIGS. 21-22 but withconsiderable differences in their effectiveness for various compounds.Cryogenic pumping is generally a continuous, nonsaturating process whichis limited chictly by the thermal conductivity of the accumulatedcondensate over the cold surface. Cryogenic pumping speed is primarily afunction of the surface area, condensation coefficient and kineticimpingement rate. The condensation or capture coefficient is a functionagain of particle impingement rate and temperature, and the surfacetemperature and coverage. The process is most effective forsupersaturated vapors.

Cryosorption pumping is obtained by the trapping of gases in absorbentmaterials at cold temperatures. The process is most effective forpermanent gases and unsaturated vapors. Porous adsorbent materials areused since the trapping process requires a fresh site for each trappedparticle, hence large surface areas are necessary to prevent saturationof the pump. Typical adsorbent materials are activated charcoal,activated alumina, silica gel and alkali metal sieves. Materialsespecially recommended for hydrogen range from charcoal to palladiumsieves.

The only coolant which is effective for cryosorption of hydrogen isliquid helium. Unfortunately, helium has a low latent heat ofvaporization (0.9 calories per cc), and is expensive, relative to LN₂.The recovery of helium gas after flowing through the cryosorptionshrouds is both highly desirable and feasible. On-site recompressionunits are commercially available.

CHLORINE PUMPING

One of the most economical sources of silicon for this process issilicon tetrachloride. The design requirements for vacuum pumping toremove the chlorine gas from the process stream after dissociation inthe anode can be approached with the same initial assumptions as forhydrogen, i.e.,

D.R.=10⁴ Å/second

A_(ss) =400 cm²

m_(Si) =100 mg/sec @ substract

m_(Si) =200 mg/sec through anode

The mass flow rate of silicon tetrachloride then would be: ##EQU64## Thepumping speed at standard temperature conditions when operating thechamber at 10⁻⁵ Torr pressure would be: ##EQU65##

As with hydrogen, this rate is not practical for ion pumps. Reduction ofthe pumping demand could be considered by lowering the deposition rate,raising the ambient pressure, or cooling the chlorine prior to pumping.

Cooling to the temperature of liquid nitrogen shrouds, would beinsufficient to obtain practical ion pumping speeds since only afourfold increase in chlorine density could be effected by thetemperature drop from the assumed 298° K. to 78° K.

This factor, combitied with the chemical incompatibility of chlorine andthe common ion pump electrode materials, will dictate the use ofcryogenic pumping when large amounts of chlorine are involvcd in theprocess chamber.

Previous considerations of this approach to cryogenic pumping ofenergetic chlorine indicate that a two-phase system will be desirable.The assumptions and calculations which led to this conclusion arerepeated here with newly assigned values of mass flow rate: ##EQU66##The net heat flux rate to the surface can be expressed as: ##EQU67##

From heat transfer considerations, ##EQU68## providing the shroudtemperature, T_(w), remains constant. Combining equations,

The residual mass of chlorine in the tank will be ##EQU69## With theassumption that the evaporation rate is small compared with theimpingement rate, this can be written as ##EQU70## and the previousequation integrates to: ##EQU71##

Values for preliminary calculations are based on the assumptions that:##EQU72## The impingement velocity now can be calculated as ##EQU73##The pumping area required would be ##EQU74## The collection lifetime ofthe surface between shutdowns for condensate removal would be ##EQU75##The mitted capacity then is no problem. The power transtuitted to thepumping surface would be ##EQU76## If only the latent heat ofvaporization were to be utilized to absorb this power, ##EQU77## Theheat flux rate on the collecting surface would be ##EQU78##

The conclusions drawn from these values are that the collector surfacearea is rather large, and the consumption of liquid nitrogen would be amajor cost element. Quantatively, if the surface area needs wereprovided by stainless steel shrouds of 1.5 meters O.D. and 0.5 metersI.D., approximately 46 double-surfaced plates would be required.

The cost of liquid nitrogen in these quantities has been quoted (in gas)at $0.43 per 100 cubic feet. At 27,600 cubic feet per ton, the cost for3612 kilograms/day day would be about $470, if no gas salvage were to bemade.

The two phase pumping system mentioned earlier would involve anintermediate surface to automatically cool the chlorine, prior toimpingement and condensation on the liquid nitrogen-cooled shrouds.

The intermediate surface could be cooled, preferably to a temperature ofa few hundred degrees Kelvin, by a relatively inexpensive liquid whichpossesses a good thermal capacity. The use of water would be mosteconomic, if suitable design and operational care is taken to preventboth freezing by the LN₂ shrouds and boiling from the received beatflux.

To examine the feasibility of the water-cooled roughing shrouds, assumethat a rather narrow range of water temperature is allowed, with inletto the shrouds at 25° C. and flow rate adjusted to limit the exitingtemperature to 50° C. The chlorine energy that is desired to be removedat this surface, through recombination and cooling, is the dissociationenergy of 6.78×10⁶ joules per kilogtam and the enthalpy increase from348° k. (based on an assumed temperature gradient across the stainlesssteel wall or 25° K., which can be iterated later by examining the heatflux and thermal conductivity) to 2500° K., at 471 joules perkilograin-°C., or 1.01×10⁶ joules per kilogram. The energy to be removedthen is ##EQU79## The mass flow rate of water for a temperature rise of25° C. and specific heat of 4.2×10³ joules per kilograml/°C. ##EQU80##

This flow rate of approximately 1 GPM is very easily achieved, and anorder or two of magnitude increase is feasible if demanded.

To estimate the heat flux at the shroud wall, assume a simplecylindrical surface along the jet centerline, of 50 cm dia by 200 cmlong. ##EQU81## which is a modest value. It is anticipated that theactual configuration of the shroud would consist of a number oftruncated conical disks containing large center holes, spaced along thecenterline so as to intersect the diffusing chlorine atoms and offerradial deflection and multiple impingement possibilities, for moreeffective cooling prior to final capture on the outer cryosurfaces.

The chlorine pumping concept then will be similar to the hydrogenconfiguration illustrated in FIGS. 21-22, with the notable substitutionof water flow instead of LN₂ through the center chevron-shaped panels,and the use of liquid nitrogen cryosurfaces in the outer array, forchlorine pumping, in lieu of the special ion pumps or liquid heliumcryosorption toroids which would be used for hydrogen.

A schematic representation of how to implement the axisymmetric massspectrograph separation feature of the processor is shown in FIG. 22.

The plasma processor 300 shown in FIGS. 22-23 has essentially the samestructure as the plasma processor 200 and corresponding elements aregiven corresponding reference numerals. The sole structure in theprocessor 500 differing from the processor 200 resides in the collectionarea. In particular, as shown in FIG. 22, the processor 300 includes acollector 311 for high molecular weight ions and a collector 313 for lowmolecular weight ions. With the addition of collector 311, coolant line283 has been eliminated and the coolant passageways have accordinglybeen slightly modified. Operationally several important new features areadded.

(i) The parameters are adjusted so that a conical collector extends intothe electromagnetic subsonic region of flow.

(ii) The conical collector electrode becomes part of the dischargecircuit. It is connected to the negative terminal of a power supply,(not shown) the positive terminal of which is connected to the cathode.The potential of this power supply is adjusted so that only ions of theheavy component of the working fluid are collected on the cone.

(iii) The conical collector must be smaller in diameter than the cathodejet, so that electrotis from the cathode jet can meet the anode sheathand flow back toward the anode, ionizing the working fluid in theanode-ionizer region. In this case the electromagnetic throat becomesannular and occurs at an axial position well downstream of the tip ofthe conical collector. It must, however, be configured to be upstream ofthe plate used to collect the low molecular weight material.

In this application of the processor materials of comparable ionizationpotential but different molecular weights can be separated. An examplewould be separation of hafnium from zirconium. Separation of thesematerials by existing chemical, and metallurgical techniques isextremely difficult, and pure hafnium is almost impossible to obtain.The important parameters for separation of hafnium from zirconium areshown in Table 9.

    ______________________________________                                                 Molecular Weight                                                                         Ionization Potential                                      ______________________________________                                        Hafnium    178.58       7.0                                                   Zirconium  91.22        6.92                                                  ______________________________________                                    

Since the ionization potentials are almost equal and the molecularweight is almost a factor of 2 different separation of these twomaterials in the processor configured to work as an axisymmetric massspectrograph should be extremely precise, accurate within 0.1%.

The working fluid can be injected as vapors or compounds, as discussedwith reference to FIG. 21. The mechanism of separation of the FIG. 22embodiment is best shown in FIG. 23 is illustrated in FIG. 23. Assume,for convenience, that the two materials injected thru the anode with thelowest and comparable ionization potentials are zirconium and hafnium.By reference to the equation 38, the mass flow rate of these materialsis adjusted to be slightly more than the critical value. They thusbecome singly ionized ions after passing thru the anode-ionizerstructure. The combined effect of the radial electric field and thesoienoidal magnetic field downstream of the anode will cause these ionsto take up radial trajectories similar to those shown in FIG. 23. Theheavier ions, in this case the hafnium, will come nearest to the centerline 325, since their inertia impedes the turning effect of the v×Bmagnetic force. Although all of the ions will have some axial velocity,on the average their radial and azimuthal velocity will be zero on theouter circle 327, which represents the anode sheath. At the next circleinward 329 on FIG. 23, the zirconium ions will have zero radial velocityand their azimuthal velocity will be a maximum at close to their Alfvenvelocity, given by equation 43. At this radial position the hafnium ionswill still have some inward radial velocity and a considerable azimuthalvelocity. No zirconium ions wil) penetrate beyond this circle 329however. The heavier hafnium ions will penetrate radially to the innercircle 331 shown on FIG. 23, where their radial velocity will becomezero and their azimuthal velocity will approach their Alfven velocity,given by Eq. 43. In order to achieve separation, then, the conicalcollector 311 must have a inaximum diameter greater than that of theinner circle 331 but smaller than that of the next circle out 329. Asthe hafnium ions strike this conical collector, the applied electricfield will keep them near the surface until their energy is reduced to alow enough value for them to become first adsorbed and then incorporatedinto the metal structure of the collector. As this layer of hafniumbuilds up on the conical collector 311, the conical collector 311 isslowly withdrawn axially through the plate collector (313) by stem 315attached to motive means (not shown) to ensure that its diameter neverexceeds that of the intermediate circle 329 shown in FIG. 23. As shownin FIG. 22, the vacuum chamber includes a substantially cylindricalextension 317 in whieb the motive means for reciprocating the conicalcollector 311 is located. Also shown therein is cooling coil 319surrounding the stem 315 which enables temperature control of theconical collector 311 to be had, and wire 321 which is connected at itsother end with cathode 105' through a power supply (not shown) with thecollector 311 having negative polarity.

The three limit circles 327, 329, 331 shown on FIG. 23 will, in reality,be smeared out into annular regions by thermal effects.

Thermal Process Annealing and Etching Using The Processor

Thermal processing and annealing of surfaces, films or layers, can beaccomplished by passing an inert gas, such as argon or helium, throughthe processor as configured in FIGS. 11-13 and having the beam 169impinge on the material that is to be thermally processed. The powerflux and thermal stabilization of the target material can be controlledin order to accomplish the desired thermal processing with the desiredsurface temperature. These thermal processing procedures can involvedual mode operation of the processor in order to incorporate nioresophistication into the time history of the energy flux rate at thesurface. In this mode of operation, if desired, the anode 127 and buffer105 may be fabricated from any one of Tungsten, Molybdenum or Rhenium.

In many applications, especially in the fabrication of semi-conductordevices, it is desirable to etch surfaces to a controlled depth. Theprocessor can be configured as in FIGS. 11-13 in order to use it as anetching machine. The major change operationally would be to pass gasesthrough the cathode and anode which, when they combine on the targetarea, from a molecule or substance that will etch the surface. Selectiveetching can be accomplished by appropriately masking the target area. Anexample could be to etch selectively some silicon from the surface of asilicon semi-conductor. In order to accomplish this the following stepscould be taken:

(1) Mask the surface with a template impervious to the etching material,e.g. platinum.

(2) Pass hydrogen gas through the cathode-buffer structure.

(3) Pass chlorine through a silicon anode structure.

(4) With appropriate coolant and radiation shielding operate the surfacetemperature at a value where the hydrogen and chlorine ions whichimpinge on the unmasked silicon will combine to form hydrogen chlorinemolecules which will etch the silicon.

Although the invention has been described in terms of detailed preferredembodiments, it should be understood that major changes may be made inthe apparatuses and methods disclosed herein without departing from thespirit thereof It is intended that the scope of the present invention belimited only by the following claims.

What is claimed is:
 1. An apparatus for depositing materials in layersby using a plasma beam electromagnetically accelerated in a vacuumcomprising:(a) a vacuum chamber and associated vacuum pumping apparatus;(b) a magnetoplasmadynamic plasma generator, the plasma generatorfurther comprising cathode means, anode means, a cathode magnet locatedin substantially surrounding relation to said cathode means; a trimmermagnet located in substantially surrounding relation to said anodemeans; a focusing magnet, at least part of which is located beyond theanode means with respect to the cathode means; (c) a shielded plasmagenerator support structure, the support structure supporting the plasmagenerator within the vacuum chamber; (d) a means to supply the plasmagenerator with electric power, the electric power being primarily directcurrent and the power enabling the plasma generator to create a plasma;(e) a target surface, the target surface being located beyond thefocusing magnet with respect to the cathode .Iadd.means .Iaddend.andanode .Iadd.means.Iaddend.; and (f) means for injecting one or more of aplurality of materials at a location within said vacuum chamber so as tofacilitate the creation of a plasma stream; (g) said plasma streamimpinging upon said target surface. .[.
 2. The apparatus of claim 1,further including an access door enabling access to the inside of thevacuum chamber from the outside, the access door having scalingmeans..].
 3. The apparatus of claim 3 wherein the means for injectingmaterials into the plasma .[.is further adapted to inject.]..Iadd.includes means for injecting .Iaddend.dopant material .[.so thatthe.]. .Iadd.for selectively applying .Iaddend.dopant material .[.may beselectively applied.]. at said target surface.
 4. The apparatus of claim3 wherein the means for injecting one or more of a plurality ofmaterials injects the materials adjacent to the cathode.Iadd.means.Iaddend..
 5. The apparatus of claim 3 wherein means areprovided so that the directional orientation of a flux pattern of thefocusing magnet can be rotated with respect to an initial plasma centerline, the initial plasma center line being a line passing through acenter of the cathode .Iadd.means .Iaddend.and a center of the anode.Iadd.means, .Iaddend.the rotation of the directional orientation of theflux pattern of the focusing magnet being effective to enable theapparatus to deposit material selectively at various portions of thetarget surface.
 6. The apparatus of claim 4 wherein means are providedso that the directional orientation of a flux pattern of the focusingmagnet can be rotated with respect to an initial plasma center line, theinitial plasma center line being a line passing through a center of thecathode .Iadd.means .Iaddend.a center of the anode.Iadd.means.Iaddend.,the rotation of the directional orientation of the flux pattern of thefocusing magnet being effective to enable the apparatus to depositmaterial selectively at various portions of the target surface. .[.7.The apparatus of claim 6 further comprising a robot means, the robotmeans being operable to move materials to and from the targetsurface..]. .[.8. The apparatus of claim 1, utilized to formsemiconductor devices..]. .[.9. The apparatus of claim 8 wherein thesemiconductor devices are silicon solar cells..].
 10. The apparatus ofclaim 1 wherein the cathode means is a thermionic cathode.
 11. Theapparatus of claim 10 wherein the thermionic cathode further includes abuffer means mounted in surrounding relation thereto, said buffer meansdefining a buffer cavity adjacent a tip portion of said thermioniccathode, and means supplying gas to said buffer cavity.
 2. The apparatusof claim 1 wherein .Iadd.said means for injecting includes means forinjecting .Iaddend.silicon .[.is injected.]. into the plasma generatorduring the operation of the the apparatus. .[.13. The apparatus of claim12 wherein the silicon is injected as a fluid compound..]. .[.14. Theapparatus of claim 12 wherein the silicon is injected as elementalsilicon in liquid form..].
 15. The apparatus of claim 12 wherein.Iadd.said means for injecting silicon includes means for injecting.Iaddend.the silicon .[.is injected.]. through the anode means.
 6. Theapparatus of claim 12 wherein .Iadd.said means for injecting siliconincludes means for injecting .Iaddend.the silicon .[.is injected.].through the cathode means. .[.17. The apparatus of claim 3, wherein thedopant is mixed with the plasma stream when the dopant is injected..]..[.18. The apparatus of claim 8 wherein top terminals may be depositedon the semiconductor devices by the plasma generator..]. .[.19. Theapparatus of claim 18 wherein the top terminals are formed by thedeposition of aluminum..]. .[.20. The apparatus of claim 18 wherein saiddeposition at the top terminals is accomplished by first having therobot means first place a solid template over the target area saidtemplate having appropriate deposition openings extending therethroughand then depositing terminal material by means of the plasmagenerator..]. .[.21. The apparatus of claim 20, wherein said terminalmaterial comprises aluminum.].
 22. The apparatus according to claim 1wherein the vacuum pumping apparatus comprises a cryogenic vacuum pumpand an ion vacuum pump. .[.23. The apparatus of claim 22, wherein saidvacuum pumping apparatus further includes a sorption pump..]. .[.24. Theapparatus of claim 11, wherein insulation means is provided between saidcathode means and said buffer means, and said means for supplying gas tosaid buffer cavity extends through said insulation means..]. .[.25. Theapparatus of claim 24, further wherein cooling means is provided forsaid cathode means and said buffer means..]. .[.26. The apparatus ofclaim 25, wherein said cooling means comprises tube means extendingwithin said cathode means and said buffer means, and means for supplyingcoolant therethrough..].
 27. The apparatus of claim 1, wherein saidcathode magnet is controllable to establish a .[.predetermined.]..Iadd.selected .Iaddend.magnetic field strength at a tip portion of saidcathode means, the magnet field formed thereby diverging away from thecathode means in the direction of said anode means.
 28. The apparatus ofclaim 27, wherein said anode means comprises a .[.ring-like.]..Iadd.ring-shaped .Iaddend.member and said trimmer magnet is adjustableto control the magnetic field within the ring-like anode means.
 29. Theapparatus of claim 1, further including upstream vacuuminsulator/isolator means mounted in said vacuum chamber between saidcathode means and said anode means.
 30. The apparatus of claim 29,wherein said upstream vacuum insulator/isolator means comprises aplurality of discs, each said disc including an outer diameter and anopening therethrough, said openings sequentially increasing in diameterfrom said cathode means to said anode means with a disc closest to saidcathode means having the smallest opening and a disc closest to saidanode nieans having the largest opening.
 31. The apparatus of claim 29,further including downstream vacuum insulator/isolator means mounted tosaid vacuum chamber between said anode means and said target surface.32. The apparatus of claim 31, wherein said downstream vacuuminsulator/isolator means comprises a plurality of truncated conicalrings of substantially idetitical configuration. .[.33. The apparatus ofclaim 32 wherein said upstream vacuum insulator/isolator means comprisesa plurality of discs, each said disc including an outer diameter and anopening therethrough, said openings sequentially increasing in diameterfrom said cathode means to said anode means with a disc closest to saidcathode means naving the smallest opening and a disc closest to saidanode means having the largest opening..]. .[.34. The apparatus of claim1, wherein said anode means includes cooling means thererer..].
 35. Theapparatus of claim 1, wherein said target surface includes cooling meanstherefor..].
 36. The apparatus of claim 33, wherein said anode meansforther includes conduit means for supplying feed gas thereto, saidconduit means being surrounded by further vacuum insulator/isolatormeans..].
 37. The apparatus of claim .[.36,.]. .Iadd.32,.Iaddend.wherein said anode means further includes conduit means forsupplying dopant gas thereto, said dopant gas conduit means beingsurrounded by .[.still.]. further vacuum insulator/isolator means, oneof said dopant gas and feed gas vacuum insulator/isolator means fortherenclosing power lead means for said anode means.
 38. Amagnetoplasmadynamic processor comprising:(a) an elongated vacuumchamber having a longitudinal axis therethrough; (b) cathode-buffermeans mounted in said vacuum chamber substantially aligned with saidlongitudinal axis and including: (i) a cathode rod; (ii) a buffermounted in surrounding spaced relation to said cathode rod; and (iii)gas supply means for supplying gas to a buffer cavity formed betweensaid cat,bode rod and said buffer; (c) an anode-ionizer mounted in saidvacuum chamber substantially aligned with said longitudinal axis andincluding: (i) an inner ring portion; (ii) an outer substantiallycylindrical portion in surrounding relation to said inner ring portion;(iii) a gap defined between said inner ring portion and said outersubstantially cylindrical portion; and (iv) means for supplying gas tosaid gap; (d) accelerating magnet means including: (i) a cathode magnetsubstantially surrounding said cathode buffer means, and (ii) a trimmermagnet substantially surrounding said anode-ionizer, and (e) upstreamvacuum insulator/isolator means mounted in said vacuum chamber betweensaid cathode-buffer means and said anode-ionizer and substantiallyaligned with said longitudinal axis.
 39. The processor of claim 38,wherein said cathode-buffer means further includes insulation meansbetween said cathode rod and said buffer.
 40. The processor of claim 39,wherein said gas supply means includes .[.thread-like.]. passagewaysextending through said insulation means and communicating with saidbuffer cavity whereby said gas is caused to swirl in said buffer cavity.41. The processor of claim 40, wherein said cathode rod includes apointed tip extending into said buffer cavity.
 42. The processor ofclaim 38, wherein said buffer includes orifice means communicating saidbuffer cavity with said vacuum chamber, said orifice means beingsubstantially aligned with said axis.
 43. The processor of claim 42,wherein said orifice means is of a size .[.designed.]. to maintain aback pressure of gas within said buffer cavity.
 44. The processor ofclaim 38, wherein said inner ring portion of said anode-ionizer includesa first end substantially flush with a first end of said outersubstantially cylindrical portion and said inner ring portion issignificantly shorter in direction of said axis then said outersubstantially cylindrical portion whereby a second end of said innerring portion lies completely within said outer substantially cylindricalportion.
 45. The .[.invention.]. .Iadd.processor .Iaddend.of claim 44,wherein said outer substantially cylindrical portion includes first andsecond orifices communicating the exterior thereof with said gap, andsaid means for supplying gas to said gap comprises:(a) First conduitmeans sealingly attached to said first orifice and communicating a rirstgas to said gap; (b) first anode vacuum insulator/isolator meanssurrounding said first conduit means; (c) second conduit means scalinglyattached to said second orifice and communicating a second gas to saidgap; and (d) second anode vacuum insulator/isolator means surroundingsaid second conduit means. .[.46. The invention of claim 45, whereinsaid first and second anode insulator/isolator means comprise: (a) aninsulative covering attached to a respective conduit means; (b) firstcylindrical means surrounding said insulative covering and spacedtherefrom; (e) second cylindrical means surrounding said firstcylindrical means and spaced therefrom; and (d) means for structurallysupporting said first and second cylindrical means in said spacedrelation..].
 47. The .[.invention.]. .Iadd.processor .Iaddend.of claim38, wherein said vacuum chamber has an annular stepped configurationadjacent said cathode-buffer means and said cathode magnet is located inoverlying relation to said annular stepped configuration.
 48. The.[.invention.]. .Iadd.processor .Iaddend.of claim 38, wherein saidupstream vacuum insulator/isolator means comprises a plurality of discs,each said disc including an outer diameter and an opening therethrough,said openings sequentially increasing in diameter from saidcathode-buffer means to said anode-ionizer with a disc closest to saidcathode-buffer means having the smallest opening and a disc closest tosaid anode-ionizer having the largest opening.
 49. The .[.invention.]..Iadd.processor .Iaddend.of claim 38, wherein said vacuum chamberextends a substantial distance beyond said anode-ionizer, and furtherwherein said processor includes downstream vacuum insulator/isolatormeans mounted within said vacuum chamber.
 50. The .[.invention.]..Iadd.processor .Iaddend.of claim 49, wherein said downstream vacuuminsulator/isolator means comprises a plurality of substantiallyidentical truncated conical segments mounted about said axis beyond saidanode-ionizer.
 51. The .[.invention.]. .Iadd.processor .Iaddend.of claim50, wherein said processor further coniprises focusing magnet meanssurrounding said downstream vacuum insulator/isolator means. .[.52. Theinvention of claim 51, wherein said focusing magnet means comprises aplurality of focusing magnets attached to the exterior of said vacuumchamber in surrounding relation to said truncated conical segments..]..[.53. The invention of claim 45, wherein said first gas comprisessemiconductor feed gas and said second gas comprises dopant gas..]. 54.The .[.invention.]. .Iadd.processor .Iaddend.of claim 45, wherein atarget means is provided in said vacuum chamber aligned with said axisat a location spaced from said anode-ionizer, and a plasma stream formedby said processor impinges upon said target means. .[.55. The inventionof claim 54, wherein constituent iotis from said first and second gasescombine at said target means to form a compound..]. .[.56. The inventionof claim 54, wherein constituent ions from said first and second gasescombine at said target means to form a mixture..]. .[.57. The inventionof claim 54, wherein constituent ions from said first and second gasescombine at said target means-to form an alloy..]. .[.58. The inventionof claim 54, wherein some constituent ions from said first and secondgases combine at said target to form one of a compound, a mixture and analloy, and wherein said processor further includes pumping means forpumping from said plasma stream and vacuum chamber constituent unionizedparticles from said first and second gases..]. .[.59. The invention ofclaim 58, wherein said pumping means comprises mechanical pump means..]..[.60. The invention of claim 58, wherein said pumping means comprisesion pump means..]. .[.61. The invention of claim 58, wherein saidpumping means comprises sorption pump means..]. .[.62. The invention ofclaim 58, wherein said pumping means comprises mechanical and ion pumpmeans..]. .[.63. The invention of claim 58, wherein said pumping meanscomprises mechanical and sorption pump means..]. .[.64. The invention ofclaim 58, wherein said pumping means comprises ion and sorption pumpmeans..]. .[.65. The invention of claim 58, wherein said pumping meanscomprises mechanical, ion atid sorption pump means.1 .]. .[.66. Theinvention of claim 54, further including cooling means for said targetmeans..]. .[.67. The invention of claim 78, wherein said cooling meanscomprises conduit means extending through said target means and supplymeans for supplying coolant to said conduit means..].
 68. The.[.invention.]. .Iadd.processor .Iaddend.of claim 38, further includingcooling means for said cathode rod.
 69. The .[.invention.]..Iadd.processor .Iaddend.of claim 68, further comprising cooling meansfor said buffer.
 70. The .[.invention.]. .Iadd.processor .Iaddend.ofclaim 69, further comprising, cooling means for said anode-ionizer. 71.The .[.invention.]. .Iadd.processor .Iaddend.of claim 70, furthercomprising cooling means for said means for supplying gas to said gap.72. The .[.invention.]. .Iadd.processor .Iaddend.of claim 45, whereinsaid first and second orifices open into said gap tangentially wherebysaid first and second gases are caused to swirl within said gap.
 73. The.[.invention.]. .Iadd.processor .Iaddend.of claim 38, wherein collectionmeans is provided in said vacuum chamber for ions of predeterminedmolecular weights.
 74. The .[.invention.]. .Iadd.processor .Iaddend.ofclaim 73, wherein said collection means comprises a first collector forhigh molecular weight ions and a second collector for low molecularweight ions.
 75. The .[.invention.]. .Iadd.processor .Iaddend.of claim73, wherein said first collector comprises a substantially conicallyshaped member mounted along said axis and oriented with a tip portionthereof facing said anode-ionizer and a base portion thereof facing awayfrom said anode-ionizer.
 76. The .[.invention.]. .Iadd.processor.Iaddend.of claim 75, wherein said second collector comprises a flatplate facing said anode-ionizer.
 77. The .[.invention.]. .Iadd.processor.Iaddend.of claim 76, wherein said second collector further comprises asubstantially circular flat plate with a hole centrally located therein.78. The .[.invention.]. .Iadd.processor .Iaddend.of claim 77, whereinsaid first collector extends through said hole in said second collectorand is substantially perpendicular to said second collector. .[.79. Theinvention of claim 51, further including a plurality of anode elementsand cathode elements mounted within said vacuum chamber in surroundingrelation to said downstream vacuum insulator/isolator means..]. .[.80.The invention of claim 79, wherein said anode elements and cathodeelements are mounted in alternating fashion with at least one anodeelement located between two cathode elements and at least one cathodeelement located between two anode elements..]. .[.81. The invention ofclaim 80, wherein said anode elements and cathode elements aresurrounded by said focusing magnet means..]. .[.82. The invention ofclaim 81, wherein said focusing magnet means is operative to: (a) focusa plasma stream formed by said processor onto target means located insaid vacuum chamber, and (b) interact with said cathode elements andanode elements to form an ion pump which pumps atoms or molecules fromsaid chamber..]. .[.83. The invention of claim 60 wherein said ion pumpmeans comprises: (a) a plurality of anode clements and cathode elementsmounted in alternating relation in said vacuum chamber between saidanode-ionizer and said target means and in surrounding relation to saidplasma stream, and (b) ion pump magnet means surrounding said anodeclements and cathode elements..]. .[.84. The invention of claim 83,wherein said ion pump magnet means further comprises focusing magnetmeans for focusing said plasma stream onto said target means..].
 85. The.[.invention.]. .Iadd.processor .Iaddend.of claim 54, whereinconstituent ions from said first and second gases combine at said targetmeans to form a doped semiconductor..].
 86. .[.The invention of claim 58wherein at least one of said first and second gases comprises aplurality of gases which are non-reactive with respect to oneanother..].
 87. .[.The invention of claim 54, wherein constituent ionsfrom said first and second gases combine at said target means to form asemi-conductor..].
 88. The .[.invention.]. .Iadd.processor .Iaddend.ofclaim 38, wherein the ion flux rate of a plasma stream formed by saidprocessor is determined by the critical mass flow rate of ions in saidplasma stream, said critical mass flow rate (m_(I))_(cr) being definedby the formula:

    (m.sub.I).sub.cr =(F.sub.EM /V.sub.cr)

where F_(EM) =electromagnetic reaction force on said accelerating magnetmeans and on all current carrying structure within said vacuum chamberV_(cr) =critical exhaust velocity of said plasma stream which equals theAlfen velocityand, further, wherein gas is supplied to said gap by saidgas supplying means at a sufficient rate to thereby provide the desiredion flux rate. . The .[.invention.]. .Iadd.processor .Iaddend.of claim38 wherein:(a) said processor further includes focusing magnet meanslocated beyond said anode-ionizer with respect to said cathode-buffermeans; (b) said processor forms a plasma stream; (c) said plasma streamis composed of a cathode jet and an anode sheath which converge at a.[.predetermined.]. distance L beyond said anode-ionizer to form anelectromagnetic throat, said .[.predetermined.]. distance L beingdefined by the formula: ##EQU82## where Φ_(A) =πR_(A) ² (B_(z))_(A)R_(A) =an inner radius of the anode-ionizer (B_(z))_(A) =averagestrength of the axial magnetic field at said anode-ionizer σ=electricalconductivity of gas in said cathode jet. k=Boltzman's constant T=Gas(electron) temperature m=mass flow rate in teh cathode jet. m_(a) =massof an atom of gas flowing in the cathode jet. I=current flowing thru thecathode jet. e=charge in the electron. ##EQU83## γ=ratio of specificheats; (d) and further wherein said term (B_(z))_(A) is a function ofmagnetic fields created by said cathode magnet, said trimmer magnet andsaid focusing magnet means, adjustment of said magnetic fields beingoperative to adjust said predetermined distance. .Iadd.90. Apparatus fordepositing material onto a substrate from a vapor phase comprising:(a) acathode; (b) an anode spaced from said cathode along an axis; (c) meansfor creating a d.c. electrical arc between said cathode and said anode,including means for creating a d.c. electric field between said anodeand said cathode and means for injecting a gas proximate said cathodefor being ionized by said electric field; (d) means for injecting aworking fluid containing a material to be deposited on the substrate ora precursor thereof into the path of said ionized gas for being ionizedthereby to form a plasma; (e) means for creating a solenoidal magneticfield between said cathode and said anode centered about said axis, saidfield diverging in the direction of and beyond said anode from saidcathode, said field azimuthally and axially accelerating the plasma withthe divergence of said solenoidal magnetic field acting to axiallyaccelerate said plasma beyond said anode in the direction of saiddivergence; (f) means for positioning the substrate in the path of saidaccelerated plasma for forming a coating of said material thereon; and(g) means for establishing a partial vacuum encompassing said arc, saidplasma and said substrate. .Iaddend. .Iadd.91. Apparatus for treating asubstrate with a material from a vapor phase comprising:(a) a cathode;(b) an anode spaced from said cathode along an axis; (c) means forcreating a d.c. electrical arc between said cathode and said anode,including means for injecting a gas proximate said cathode for beingionized by said arc; (d) means for injecting a working fluid into thepath of said ionized gas proximate said anode for being ionized therebyto form a plasma, said working fluid including the material for treatingthe substrate or a precursor thereof; (e) means for creating asolenoidal magnetic field between said cathode and said anode centeredabout said axis, said field diverging in the direction of and beyondsaid anode from said cathode, said field azimuthally and axiallyaccelerating the plasma beyond said anode in the direction of saiddivergence; (f) means for positioning the substrate in the path of saidplasma for being treated by said plasma; and (g) means for establishinga partial vacuum encompassing said cathode, anode, injected gas andworking fluid and substrate. .Iaddend. .Iadd.92. The apparatus of claim91 wherein said means for injecting a gas includes means for azimuthalinjecting said gas about said axis, and said means for injecting aworking fluid into said ionized gas includes means for azimuthalinjecting said working fluid about said axis. .Iaddend. .Iadd. Apparatusof claims 90 or 91 wherein said means for injecting a working fluidincludes means for injecting said working fluid azimuthally about theaxis of said solenoidal magnetic field. .Iaddend. .Iadd.94. Theapparatus of claim 91, wherein the means for creating a solenoidalmagnetic field comprises an accelerating magnet adjacent to the cathode..Iaddend. .Iadd.95. The apparatus of claim 91, wherein said means forcreating a solenoidal magnetic field comprises a cathode magnet locatedin substantially surrounding relation to said cathode. .Iaddend..Iadd.96. The apparatus of claim 91, further including a trimmer magnetlocated adjacent to said anode. .Iaddend. .Iadd.97. The apparatus ofclaim 91, further including a focusing magnet located between said anodeand said means for positioning the substrate. .Iaddend. .Iadd.98.Apparatus for depositing material onto a substrate from a vapor phasecomprising:(a) a cathode; (b) an anode spaced from said cathode; (c)means for creating a d.c. electrical arc between said cathode and saidanode, including means for injecting a gas proximate said cathode; (d)means for injecting a working fluid proximate said anode with a velocitycomponent tangential to a circle normal to the axis of the solenoidalfield and for ionizing said fluid to form a plasma, said ionized fluidcontaining a material to be deposited on the substrate or a precursorthereof; (e) a plurality of magnets including an accelerating magnetadjacent to said cathode, a trimmer magnet located adjacent to saidanode, and a focusing magnet located beyond said anode from saidcathode; (f) means for positioning the substrate in the path of saidplasma beyond said focusing magnet for forming a coating of saidmaterial thereon; and (g) means for establishing a partial vacuumencompassing said cathode, anode, injected gas and working fluid andsubstrate. .Iaddend. .Iadd.99. A method for depositing materials on asubstrate comprising the steps of:(a) establishing a d.c. arc along anaxis between a cathode and an anode spaced from said cathode along saidaxis including injecting a gas for being ionized by said arc; (b)ionizing a working fluid containing a material to be deposited on thesubstrate or a precursor thereof to form a plasma by injecting saidfluid into the path of said ionized gas; (c) azimuthal and axiallyaccelerating the plasma beyond said anode from said cathode bysubjecting said plasma to a solenoidal magnetic field centered aboutsaid axis, said field diverging in the direction of and beyond saidanode from said cathode; (d) coating the substrate with said material bypositioning said substrate in the path of said accelerated plasma; and(e) establishing a partial vacuum in the region encompassing said arc,said plasma and said substrate. .Iaddend. .Iadd.100. A method fortreating a substrate with a material from a vapor phase comprising:(a)creating a d.c. electrical arc between a cathode and an anode spacedfrom said cathode along an axis including injecting a gas proximate saidcathode for being ionized by said arc; (b) injecting a working fluidinto said ionized gas proximate said anode for being ionized thereby toform a plasma, said working fluid including a material for treating thesubstrate or a precursor thereof; (c) creating a solenoidal magneticfield between said cathode and said anode centered about said axis, saidfield diverging in the direction of and beyond said anode from saidcathode, said field azimuthally and axially accelerating said plasmabeyond said anode in the direction of said divergence; (d) positioningthe substrate in the path of said plasma for being treated by saidplasma; and (e) establishing a partial vacuum in the region encompassingsaid cathode, anode, injected gas and working fluid and substrate..Iaddend. .Iadd.101. The method of claim 100 wherein said gas and saidworking fluid are injected azimuthally about said axis. .Iaddend..Iadd.102. The method of claim 100 wherein said plasma forms a coatingof said material on said substrate. .Iaddend. .Iadd.103. Apparatus forpracticing the method of claim 100 for treating a substrate with amaterial from a vapor phase, comprising:(a) a cathode; (b) an anodespaced from said cathode along an axis; (c) means for creating a d.c.electrical arc between said cathode and said anode including injecting agas proximate said cathode for being ionized by said arc; (d) means forinjecting a working fluid into said ionized gas proximate said anode forbeing ionized thereby to form a plasma, said working fluid including amaterial for treating the substrate or a precursor thereof; (e) meansfor creating a solenoidal magnetic field between said cathode and saidanode centered about said axis, said field diverging in the direction ofand beyond said anode from said cathode, said field azimuthally andaxially accelerating said plasma beyond said anode in the direction ofsaid divergence; (f) means for positioning the substrate in the path ofsaid plasma for being treated by said plasma; and (g) means forestablishing a partial vacuum in the region encompassing said cathode,anode, injected gas and working fluid and substrate. .Iaddend..Iadd.104. Apparatus for separating a higher molecules weight materialfrom a lower molecular weight material in a vapor phase comprising:(a) acathode; (b) an anode spaced from said cathode along an axis; (c) meansfor creating a d.c. electrical arc discharge, between said anode andsaid cathode, including injecting a gas proximate said cathode for beingionized by said arc discharge, said anode being configured for causingsaid arc discharge to extend along said axis beyond said anode from saidcathode; (d) means for injecting a working fluid into the path of saidionized gas for being ionized thereby to form a plasma, said plasmacontaining ions of said materials to be separated; (e) means forestablishing a solenoidal magnetic field about said axis, said fielddiverging in the direction of and beyond said anode from said cathodefor azimuthal and axially accelerating said plasma beyond said anode inthe direction of said divergence; (f) a first surface positioned in thecentral portion of said plasma, centered on said axis for depositing thehigher molecular weight material thereon; (g) a second surfacepositioned in a peripheral portion of said plasma surrounding saidcentral portion for depositing said lower molecular weight materialthereon; and (h) means for establishing a partial vacuum in the regionencompassing said cathode, anode, arc, plasma and first and secondsurfaces. .Iaddend. .Iadd.05. The apparatus of claim 104 wherein theportion of the arc discharge extending beyond said anode includes acathode jet and an anode sheath, and wherein said first surface extendsinto said cathode jet. .Iaddend. .Iadd.106. The apparatus of claims 90,91, 98 or 104 wherein said anode includes a substantially cylindricalhollow portion extending axially downstream away from said cathode forassisting in the ionization of said working fluid. .Iaddend. .Iadd.107.The apparatus of claims 90, 91, 98 or 104 further including vacuuminsulator/isolator means between said cathode and anode. .Iaddend..Iadd.108. A method for separating a higher molecular weight materialfrom a lower molecular weight material in a vapor phase comprising:(a)establishing a d.c. electrical arc discharge between a cathode and ananode spaced from said cathode along an axis, said arc dischargeincluding an ionized gas and having a portion extending along said axisfrom said anode in the direction away from said cathode; (b) ionizing aworking fluid to form a plasma by injecting said fluid into the path ofsaid ionized gas, said ionized working fluid containing ions of suchdifferent molecular weight materials to be separated; (c) establishing asolenoidal magnetic field centered about said axis, said field divergingin the direction of and beyond said anode from said cathode, said fieldazimuthally and axially accelerating said plasma beyond said anode inthe direction of said divergence; (d) depositing the higher molecularweight material on a first surface located in the central portion ofsaid plasma centered on said axis; (e) depositing said lower molecularweight material on a second surface located in a peripheral area of saidplasma surrounding said central portion; and (f) establishing a partialvacuum in the region encompassing said cathode, anode, arc discharge,plasma and first and second surfaces. .Iaddend. .Iadd.109. The method ofclaim 108 wherein said portion of said arc discharge extending beyondsaid anode includes a cathode jet and an anode sheath, and wherein saidstep of depositing the higher weight material includes collecting saidhigher molecular weight ions on a surface extending into said cathodejet. .Iaddend.